Just use an old PC or laptop if you have one. If not install VirtualBox and give the different distros a try. It'll run slower than if it was on actual hardware but it'll let you try the OSes until you find something that you like.

Yep, as a Mac user for 34 years, KDE is too Windows-like and Gnome felt pretty similar to Mac.

I like KDE but it's a little too Windows-like and very busy/cluttered, that's why I prefer Gnome as it feels closer to Mac OS (which use at work).

When you get your passwords, I'd suggest using Bitwarden as it has browser extensions and doesn't tie you to a certain browser.