Just a couple minor points to add to your consideration. IDK what your budget is but buying a used flagship camera is often better than a new midrange camera. The main difference you’re going to not be able to easily compete with is newer sensor tech but there are some really stellar older cameras.
You don’t mention what kind of photography you’re trying to do and that would make difference.
I picked up a used canon 7D mark 2 for about $350 used it basically perfect condition. Because this was a prosumer flagship at the time it has all the bells and whistles of that era. It’s my primary wildlife camera. I picked up an Olympus OM-D E-M5 2 recently for about $450. Their prices have bumped up a lot I think because everyone is getting into street photography. I’ve been having lots of fun with it. Got a 7.5mm Rokinon fisheye and a 14-42mm zoom. Been fun doing closeups on insects and landscape stuff so far. It’s very compact and feature rich. M43 lenses are much cheaper entry point than APS-C and FF are so for just having fun it’s way cheaper to experiment. Having IBIS is really nice too.
Both cameras have tons of customizaility. They aren’t the low light champs a full frame would be but getting some faster primes has helped with that. I picked one up from UsedPhotoPro and the other from MPB. They do a good job going over the cameras and showing you the exact one you’re purchasing and they offer 6-12 month guarantees on all the stuff they sell which is nice.
It sounds like you really want something lighter weight so M43 might be a good way to go. There are some really nice cameras in M43. The prices even new are less. Flagship Sony, canon, Nikon are all in that 5-7000 range and flagship Olympus and Panasonic are like 2000-2500 new. Something I decided was to get a used M43 knowing that because it’s an open standard any lenses I got would mostly work between Olympus and Panasonic if I upgraded to a new body. It’s also a good way to get a “pro” style more DSLR like body if you want and a super small pocket camera style at the same time and have a collection of lenses to choose from as the whim suits.
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Okay either you edited while I was typing or I didn't see before what you said your types of photography were.
As happy as I have been with my canon DSLR... I agree with you ( and many others ). Canon's policy about 3rd party lenses is utter bullshit... and their first party glass is way overpriced. Only their L glass can really outshine anyone and it's stupidly overpriced... their regular stuff you're better with sigma and since their new R system stuff doesn't play nice with that it's a non-starter really. (Now if you wanted to go with DSLR, it's a different story but those are chunky and heavy... my wildlife rig weighs 8-10lbs depending on what I bring for just the camera itself)
With you starting your post about camera size and mentioning the nikon d3200.. which isn't a large DSLR... I really think the M43 format might be worth looking into. Another big advantage of M43 is even if the body is the same size, the lenses will be considerably smaller and lighter than comparable APS-C or FF lenses. So size and weight will be greatly reduced. The crop factor on M43 is 2x (as opposed to 1.5x nikon APS-C and 1.6x canon APS-C) so getting more "reach" with a lens for things like birds is easier with smaller focal length glass as well. Since most of them will have good IBIS since it's easier to stabilize physically smaller sensor as well. Not that new APS-C and FF cameras can't have good IBIS.. but for example my OM-D E-M5 2 has several stops of 5 axis IBIS on a camera from 2015. I can handhold shots at 1/2 second shutter speeds. Newer cameras will be even better. For hiking et al, the smaller size and weight will be a bonus. For street photography it's one of the go to systems because of the small size. Etc.
The 4K video is going to be a stickier subject and looking into hybrid cameras is much trickier. I recommend checking out petapixel's youtube. That's where the DPReview guys ended up and their stuff is great. It focuses on both still and video so a review of anything will be well rounded. https://www.youtube.com/@PetaPixel for their older stuff DPReview is still around for now as well https://www.youtube.com/@dpreview I also really like MicroFourNerds stuff if you wanted to look at a ton of different reviews focused on M43 system. https://www.youtube.com/@MicroFourNerds
I agree that point and shoot or bridge cameras are a a little silly these days. I have been looking into the M43 stuff because I can add a few different sized and featured bodies while sticking with interchangeable lenses that are part of the same system. Some of the M43 bodies are absolutely tiny, especially if you're willing to give up the viewfinder and only use the back screen.
I saw you mention in another reply about how the newer M43 seem to be not doing compact cameras anymore. It's hard to say if that trend will continue or not... panasonic seems to be doing more of that sort of thing still and offering things across the spectrum of use cases. I feel like the popularity of street photography right now will likely make some new compact things show up eventually. I would point out, also, that the sony a7iii you're mentioning is basically the same physical size as the OM-1 series... but the lenses will be half the size. https://camerasize.com/compare/#777,918 so your total kit size and weight will be much smaller.
I watched countless videos looking at little M43 cameras before I picked up the E-M5 II. The weather sealing was definitely a big bonus for a little camera. I don't care about video at all, so I was happy to go with the slightly older version. The better hand held "high rez" on the E-M5 III is nice, though I've heard the build quality is a little more plasticy. Personal preference really.. .it does reduce weight a bit. As for image quality... I have been very happy with my results. This is one of the first cameras where I've been mostly happy with the JPEGs that come directly out of camera. I still shoot RAW+JPEG but I find myself only editing occasionally when sharing which is nice.
Don't get me wrong, the stuff that comes out of sony SLR style cameras is really good. They definitely do some good stuff in their sensors. And if you get their G series lenses, they are very nice... but expensive. You've just mentioned the size and carry weight a bit and I've fixated on that. When I'm out birding, I always run into other people as well... and the rigs that people are carrying for sony, nikon, and canon are all the same size. A lot of people carrying 150-600 or 100-400 lenses... and they're huge. That was one of the motivations for wanting a second camera and adding some M43 into my lineup.
One of the things that I have done with camera and lens purchases is go to flickr. You can search hashtags by item name. So when I was looking for M43 I was comparing the omd em5 ii vs the lumix gx8... so I just searched for those and you'll get a bunch of real world photos that people have taken to see what things looked like. Same thing for lenses... searching for a lens make and model... and you'll see that lens how it looks on multiple different bodies. A good quick way to compare a lot of real world stuff and not the clinical shots that reviewers use. Both are useful.
The advice I've always received, and it makes sense to me, is pick a lens system. Lenses hold value and last longer than camera bodies, especially with digital. So if there is a system that has a lot of lenses you like and options (seriously fck canon and their no 3rd party rules) it makes sense to get those and get a body to match.
Good luck on the search. Try not to let the spec overload get to you... at the end of the day most cameras are pretty good these days. Once you've narrowed to some of the better ones, anything you choose will likely make you happy. :)
--edit-- Added a full rez image from the first day I had the EM5II taken with the 14-42mm kit lens. Unedited JPEG out of camera just so you can see the detail, as that was a concern you voiced.