Avidemux

A new version (2.8.0) is out: https://sourceforge.net/projects/avidemux/

This page says "OS X 10.10.0 or later", but when you go to their page the only 2.7.8 version of the app for macOS they have requires Catalina (and I did try to download it to see would it maybe run on earlier versions, but it just tells you that it requires Catalina or newer version of macOS)... it seems kind of preposterous when some app that doesn't really seem to need some Catalina specific frameworks like CoreML3 or something similar is just requiring Catalina like that, even though it probably doesn't really need anything which isn't available on earlier versions of macOS... and if they only have one Mac that is running Catalina to test the app on, instead of deciding to just require Catalina, they could have just installed an earlier version on a different partition or at least in a VM if that Mac was too new to support installing a version before Catalina on another partition... Many Mac users will probably stay on Mojave or High Sierra for a while because of the 32-bit support (there might not be many apps that are 32-bit only and didn't get an update to 64-bit that many users need, but if someone really needs some app and it doesn't have a 64-bit version, one such app could be enough to make someone stay on Mojave, until someone can find a suitable replacement for it)... and if some app doesn't really need any frameworks that are only available on Catalina and Big Sur, it shouldn't try to make users upgrade to Catalina and Big Sur to use it.

If what you want to do is just trim video, this is very easy to use.

When I use this app I always have some problems... I used to use it a lot, now I’ve abandoned it.

The last version running on OS 10.9 is 2.6.14.
The most recent ones are all labelled "Sierra_64Bits", including the last 2.6.18, so I suppose they only run in that OS.
N.B.: version number only shows in the app, not in the Finder

Current version is 2.6.10. I haven't found any compatibility information but as the file name contains ML, guess what... ;-) At least, I can say it works in OS 10.9.5. A not very intuitive XP like GUI but it works for simple trimming, cutting or concatenating. Don't forget to specify the output format before saving. ;-) I haven't found many free apps to concatenate mp4 files without having to save them in a different format but this is one of them (the other one is SmartCutter — not present in MU and with an even more XP look than Avidemux! :-D).