y question is “why?” It seems like, at a basic level, they serve similar roles. If you remove the app-platform role from Nextcloud by separately hosting the individual apps, what benefit do you get from having both Nextcloud and File Browser?

NextCloud sucks, it overpromises, underdelivers, wastes resources and has tons of issues and stupid bugs like these. If you simply setup FileBrowser + Syncthing you’ll get a much better experience for way “cheaper”.