Free and Open Source Software

Honestly, on mobile, there isn't really anything. However, if you're burdened with an iPhone (like me), I'd say use iMovie.

If you're on Android and you're clever, you might be able to use FFmpeg from inside Termux.

If you have a particularly powerful phone, you might be able to install a window manager (most people go for Fluxbox) and a lightweight video editor (like Avidemux) in Termux, share your screen with a TigerVNC daemon, and then use a VNC client on Android to access it. It will most likely be slow and a little choppy, but it might just work if you seriously have no alternative.

There is ffshare which at least allows compressing.

Maybe some Gallery app can? Simple Gallery and Amaze Tools cant. Signal can cut videos but yeah. Telegram too.

Its pretty crazy that the best video editor is probably in Tiktok

The closest I know of is not completely free or open source, but it’s by Ubiquiti Labs and it’s really good for a mobile video editor. Mentioning it because it might still meet some people’s criteria:

VN →

Video Transcoder on F-Droid allows you to convert and cut videos at least, but it hasn't seen an update in ages and the cutting process isn't 100% precise, so you might end up with +- a second of what you intended.

No

I don't think so.

I don't think so, but maybe you could set up remote access with a desktop and use OpenShot?