Believe it or not, I occasionally use FFMPEG inside Termux on my phone. Is it easy? Hell no. You have to read the manual to do the most basic thing. But it’s really powerful and it’s FOSS.
Usually I just cut part of a video down to a few seconds of maybe crop off some black bars. That kind of thing. Or extract the audio to an MP3. (If it’s a song you’re going for, you can snag just the audio from YouTube with yt-dlp without the need for FFMPEG.)
If it had a front-end to help with finding timestamps and crop dimensions, that’d be great.
Oh, and I occasionally convert a video from webm to mp4 to send it to my friends on iPhone since Signal for iPhone can’t seem to play webm videos. That kind of thing is pretty quick and easy.