To be honest I haven't owned a dGPU in almost 20 years, but I've been lead to understand that most users with them use them all the time and ignore their iGPU, unless they're laptop users, in which case they might have to use Nvidia's proprietary drivers from what I understand; the installation of which is something Mint makes straight forward for novices, or so I've been lead to understand. Maybe I'm wrong about some of that.

I definitely agree that KDE vs Cinnamon probably doesn't matter. But I'm afraid I don't think particularly highly of any KDE-first distro; it's great from, for example, OpenSUSE, but that's not a distro I'd recommend to new users for other reasons.

The problem I've got with Ubuntu is they keep doing weird shit like submitting desktop searches to Amazon or putting ads in the motd. They're an erratic organization and I think it's a mistake to send new users in their direction. Mint may not be perfect, but I think it's broadly inoffensive and mild, a good distro to leave a good first impression on a new user fumbling through the process themself.