Ubuntu or Mint
Probably depends how you define things. Like, is Xubuntu Xubuntu or Ubuntu with Xfce included by default? How much change is necessary before it’s not “debian with added bits”?
There is not a reliable way to determine that, by design.
If we are talking about desktop PCs, maybe Ubuntu, but based these reports it’s Arch.
Worth keeping in mind that the steam deck uses a distro based on arch, so it might be inflating the arch numbers in that steam survey.
Chrome OS.
If you count Ubuntu and all disto’s base on it as one, then it would top the list.
define “most popular” please
for instance https://distrowatch.com/dwres.php?resource=popularity, does that metric fit your definition?
Anyway whatever the answer it doesn’t really matters, at the end of the day it is always Linux anyway, regardless of package manager, desktop environment or init.
I’d just warn you against Ubuntu, because its company Canonical is behaving a lot like a young Microsoft these days.
PC deez nuts
MX Linux
Source: https://gitnux.org/most-popular-linux-distributions/
It’s the most popular on Distrowatch but definitely not in real life
Disteowatch is an unreliable source since it’s basically just a giant tracker for its own sites.