I'm a recent convert from Gnome. Mostly cause Gnome seemed to have too many mysterious crashes—waking from sleep, switching between windows when video was playing—so much so that it was just easier to switch to something modern (as opposed to sway/i3) and not have to learn/rewrite keybindings.

I remember once in college I'd shared my phone's hotspot to connect a TV to the internet after it had abruptly stopped working. And all of a sudden the ads being shown (on YouTube) switched from the local language to mine, both of which are completely different.

The combination of IP, language preference and available fonts is very potent and not obvious to Americans.

Nope. Running microG on CalyxOS

You did say you were using your phone as a "hotspot" so identity info may not necessarily be leaking from the phone itself.