I disagree about the UX but that is probably just my preference. I use Facebook marketplace sometimes and it seems fully functional, no jumping around or whatever. Every now and then I have to use desktop mode but only on like government sites. Maybe it’s because I use an ad blocker that I don’t notice the problems you report.
I’m adding debian to the drive on a ten plus year old laptop as we speak. It’s taking forever because I have to do part of it manually but usually it takes less than an hour and is mostly idiot proof (my current project is on its 3rd week so I am just a special kind of idiot) but a small lightweight distro alongside the windows partition is an easy way to give old hardware new life without migrating data.
It does. I have an old Verizon phone as the white noise player / HA control in my kids bedroom. You will have all the bloat and whatever other services they install in there too though.