Graphene will likely ignore the EU, as will most Linux distros having no EU connections. Graphene’s very picky about hardware, which is why they stick with the Pixel, but anyone with the cash can pay an OEM to make a phone to their specs and install whatever Android or Linux mobile variant they want, then make 1000 or 10,000 of them to sell.
These kinds of laws will not succeed. People will choose to ignore them, like they ignore other laws, like they litter, jaywalk, drive 10 over the limit, run stop signs, etc. It will succeed in driving up prices on products from those companies who choose to comply, because they will be forced to hire in a lot more lawyers and compliance staff. These laws create lots of full time jobs in tech companies that few realize even exist. They have meetings every week, attend conferences, constantly send letters back and forth to each other. Then people wonder why their Gamepass fees went up $10 (its not actually the games)
I’ve been using Linux and Graphene for a long time and welcome all third party OS phones not controlled by Google and Apple. Jolla never marketed theirs in the USA and it always seemed more like a prototype phone for hobbyists more than a daily driver (same as all of the others).
This will probably continue to be the case until someone with deep pockets in the USA does a deal with a friendly phone OEM who makes a decent quality product and a mobile OS group who can make it at least as user friendly as Android. Considering the Byzantine labyrinth that Android’s user interface is today, the last part should not be that difficult.