Hard to find raw numbers backed by good sources.

If you filter the Steam Hardware Survey for December 2023 by Linux, you can see Arch has a market share of 7.85% (excluding SteamOS on the Deck, which is technically based on Arch and has 40.53%) while Ubuntu 22.04.3 LTS - a specific Ubuntu version - already has 7.04% on its own.

But that’s also just Steam users. Ubuntu is one of the few Linux distributions that OEMs ship preinstalled and officially support on some of their devices (Dell for example). Another example is Fedora iirc, which Lenovo ships or at least used to ship as an option on some of their ThinkPad notebooks.

I’d assume the Arch community on Reddit is bigger than the Ubuntu community as it’s geared towards tech-savvy people. Going by Reddit community size wouldn’t make much sense though. Even if you add up the member count of the r/windows, r/windows10 and r/windows11 community (which doesn’t make a lot of sense as most users are probably not unique), it’s only like 3-4x the members of r/archlinux, which doesn’t translate to market share whatsoever.

I don’t really have hard numbers, sorry. Should’ve checked first. I guess I just assumed because of the OEM support and being relatively easy to install and maintain for the average guy (in comparison) that it was the leading Linux desktop distro in terms of marketshare. I’m still assuming this is the case for the reasons stated, but can’t tell you with 100% certainty.