Ubuntu is a pretty good substitute for macOS. My key issue with Linux is the small selection of productivity apps: markdown editors, code editors, drawing packages, password managers like 1Password. Feature rich terminal apps like iTerm2. Well designed Git UI clients like Tower etc.
The rest is pretty good. Like the core UI, file manager, virtual desktop management, configuration etc works very well. Much nicer than the Windows mess.
I've been using 4k with linux for years. On large desktop screens I don't find fractional scaling to be necessary. The important text in apps that matter like terminals, text editors and browsers, chat clients, etc, has always supported scaling well. The only thing that lacked support were system dialogs and title bars. 2x was fine for those until fractional support came out in gnome recently.