Thanks for the extra inputs.
Interesting. Indeed, XFCE (used by Xubuntu) has not migrated to Wayland yet (and does not seem too keen on doing so AFAIK, even if there’s talk and tests about it).
I hope not as well, but they look basically the same on my older laptop. But…
… maybe I’m just too used to muted colors? 
But the way the built-in profile seems to skew stuff towards red-orange, and the fact that some Firefox users observe the same thing and find it as weird as I do, tend to make me think that my eyes are not deceiving me. 
Woops, I wrote my explanation blurb for Ardèche (France), 14–17 July 2025 in such a rush (had to catch a train) that I forgot to tell people to warn me if colors seemed oddly warm to them. I’ll maybe add it now but it’s a bit late for that now. 
And it’s already so long that I doubt people read the whole thing.
Sadly (or funnily) enough, it’s on my Fairphone 3+ that my pics look the best. 
And it seems to be somewhere between my laptop’s “with-profile” and “without-profile” versions. It has a (naturally?) higher contrast so it’s hard to tell for sure. I don’t know what to think.
Gemini says that the default profile I see is generated by colord “by reading the monitor’s EDID (Extended Display Identification Data)”. Apparently, this is generally far from perfect but should not be utterly wrong either… but can bring an odd warm or cold tint too in some cases. It also considers that since my external monitor is an IPS monitor, I should be able to trust it more that the built-in one, even with the auto-generated profile. 
Also, this is apparently a known limitation of Firefox on Linux that it uses the laptop’s built-in screen profile even on external monitors.
Perhaps I should start considering calibration, but the “potentially expensive” part makes me wonder if it’s worth it at my level. I mean, my edits do not look terribly off to me no matter the device I check them on, and I don’t do that for a living. And I guess that even if I have to print stuff in years and if RawTherapee (God forbid!!) dies, it is possible to do soft-proofing to some extent from the 16-bit PNGs I intend to back up. (And I haven’t looked for a way to use the resulting profile as a working profile for RT with the AppImage version, but I suppose there’s a way.)