Pretty much everything. I only had 4GB ram until two or three years ago. No swap. Never ran into an issue.
I have 8GB, which I've had since 2012. Never had a problem - I run a lean Nixos with just xmonad and dmenu, chrome, emacs, and about a dozen open pdfs and video tutorials.
>I only had 4GB ram until two or three years ago. No swap. Never ran into an issue
That sounds like an problem Windows could solve.