So I do a lot of video editing and I've been trying to use open source stuff where possible (I hate Premiere before it was cool). There's two tools I would like to share with you all that you might find helpful.
Lossless Cut
Website: https://mifi.no/losslesscut/
Github: https://github.com/mifi/lossless-cut
Losslesscut is a video remux that allows you to cut up videos into subclips, condense, or even add markers to an mkv/mp4. A big help if you record for a long time in obs as an example. Before hybrid mp4 was added I used this to remux my MKV videos to MP4s all the time since I was going to cut up my gameplay anyways. Even then still usefully if you want to clip something you recorded, and not lose quality from a retranscode. Also lets you replace audio streams if need be.
Shutter Encoder
Website: https://www.shutterencoder.com/
Github: https://github.com/paulpacifico/shutter-encoder
Shutter encoder is maybe one of the best FFmpeg GUIs I've seen if you're not used to the commandline syntax (hi that's me). It also comes with a bunch of additional features such as yt-dlp, dvdauthor, and some ai upscaler called Real-ESRGAN ncnn. Personally I only used it to extract & convert audio from video, but anything that you want to do in FFmpeg you can do this in this. Useful if you need to do more than what you can do in handbreak.
