Linux

It sounds like you'd be better off with a DE or WM that isn't gnome. The GNOME Project has been progressively sticking more and more of the customization features of the DE behind either gnome tweaks or the command line, likely to unify the experience for all users and improve the ability to provide support.

Personally, as far as gnome-based DEs are concerned, I prefer cinnamon, but I'm fine running Mint to just have it come pre-installed. I don't know what dependencies it pulls in now if you install it standalone from Mint.

That part is stupid indeed. If you run X, do xinput and find your trackpad. Then do xinput list-props on that to see all the settings there are. Xinput can also change them with xinput set-prop and they reset after a reboot, so feel free to fiddle around.

Once you're done, just slap your settings into a script and run that on startup, then you're set.

What

You're using software that's being continuously developed by people for whom stability of the UI is not a priority. Pointless UI churn is normal. Half-assed solutions kept beyond their best-before date are normal. Windows does this crap too. At least with Linux you have a choice of which issues you're going to tolerate (or you can pick a DE where UI stability is a priority for the development team).

At least KDE is planning to introduce customisable trackpad gestures next year, with Plasma 6.0. Not sure if that would include palm rejection though or the other stuff.

I don't think you can adjust scroll speed on Gnome without Gconfig

You might check out xfce. It's gtk like Gnome but the development team doesn't have their heads up their asses; pretty much every aspect of xfce can be customized. It should be a simple install from your package manager, whatever distribution you're using. The downside of this, however, is it might take extensive tweaking to get it to look how you want as it's a pretty bare bones UI by default. Personally I like it, but ymmv.

That's the beautiful thing about the Linux world. If you don't like some aspect there's virtually always an alternative.