FWIW, I also don't use any fancy collection management and barely understand what all these Lightrooms and XMP files are for. Maybe I should, but up to this day photos for me are just a bunch of files in the folder, that I sometimes manually group into subfolders like 2025-09, mostly to make it easier on thumbnail-maker.
It keeps the originals locally when it uploads forever unless you delete them. There's a one click "free up space on this device" button to delete the local files. It's actually somewhat annoying to export in bulk, you pretty much have to use takeout.