It isn't open source, but DaVinci Resolve is available for Linux. With limited features if you don't pay. Might be overkill for what you do, and I understand it can be finicky to get it working (needs nvidia, poor support for AMD, very limited format support unless you get the paied version, ...).
I don't really do video stuff, but I did play around with it a few years ago, and it seemed very comprehensive.