Export unmodified videos

Photos doesn't change the original upload. (Well, except for the file name to keep in unique-- but it will remember the old file name and use it transparently.) Videos are notoriously non-standardized, and codecs change, and some become obsolete, so there are some formats that must be converted in order to keep them in Photos -- but if you can load it, the original will still there. Here is something I have from 2004:

While I can do some video editing in Photos, I can always use "Export Unmodified Original" to get the exact file back.

I must say that I'm not sure that I see Photos as the ideal place to store anything more than short simple videos. For videos more than a few minutes, I just keep them in Finder folders, and I view them in whatever works this year.

Export unmodified behaves the same with images and movies. I.e. you get the same pixel data and metadata that was imported.

Any metadata edits go to Photos database and can be exported with .xmp sidecars (with nonstandard GPS).