My setup for photo and video was for quite some time:
GrapheneOS Camera (for photo and video), Aves (as a gallery app), ImageToolbox (for image editing - if the stock app isn't enough) and Open Video Editor for editing videos.
The rest of the setup was great, but the Open Video Editor has its weaknesses (especially for trimming - scrolling through the timeline the preview often didn't fit - so trimming became a game of luck).
There are already some discussions about this. For me personally, the apps mentioned there did'nt work, but maybe you find the suggestions helpful:
https://discuss.grapheneos.org/d/4369-video-editor-recommend-for-graphene
https://discuss.grapheneos.org/d/12853-fairly-private-video-editor-i-think
At some point I went back to Google Photos (image + video editing) and switch back and forth between GrapheneOS Camera (I actually like its photos better because of the more natural look) and Pixel Camera (especially in low light Pixel Camera does a great job in noise reduction, portraits, pictures with moving subjects (as i find AF more reliable, especial with people), slow-motion videos).
But I wouldn't mind uninstalling Google Photos either, so I second your question: If anyone has a good workflow or knows a decent video editor (ideally open source), please let us know.