2024 is the Year of Linux on the Desktop, at least for my boyfriend. He's running Windows 7 right now, so I'll be switching him to Ubuntu in a few days. Ubuntu was chosen because Proton is officially supported in Ubuntu.
Like others already mentioned, I would suggest Linux Mint as well. It's better Ubuntu than Ubuntu and similarity to Windows UI would make his transition much better.
Seconded. Switched my wife to Mint two years ago, and she never cared about going back to Windows. Not that she cares about Mint, either; the point of contention was the transition, which was much smoother than she was afraid of.