That page was indeed interesting, I didn't know about environment.d.
Sadly, it's not something I can use, as I actually need to source a script myself to set those variables, and environment.d allows only key=value entries (it's not a script, it's a configuration file).
Possibly xprofile is what I want. Would that break anything in Solus? (I have pretty much no experience messing with those configurations and Solus is not Arch 😅 )