Computers were either Windows or Mac, they couldn’t be anything else, that was a fact. Then I saw someone using Linux and had so many questions. How? I was given a Knoppix live CD, went home, and booted my home PC into Knoppix and it changed my perception of computers.
I didn’t change over immediately but eventually Ubuntu was handing out install CDs and YouTube was full of wobbly windows and desktop cubes. It wasn’t useful but it looked cool.
I still needed Windows for gaming, but for day to day it was so much easier to use Linux.
Eventually my gaming was exclusively on the Switch and then was I was looking to play certain PC games the Steam Deck was available, so I bought that.
I think Windows 8 was the last one I used and I’ve never had any desire to go back. Linux is just easier.
I would suggest whatever you pick, it should be a similar base to what you run or are most familiar with.
If you run something Debian based, you should recommend something Debian based. Fedora, Arch, etc.
The same is also true for desktop environments, if you use KDE, recommend KDE. If you run something not necessarily beginner friendly, recommend what you’re familiar with.
At some point you’re going to be asked questions, so the more familiar you are, the better for both of you.