I'm pretty sure GrapheneOS plans to have GUI Linux applications via the terminal app. I probably wouldn't go with a Pixel 3a but I've been considering picking up a users OnePlus 6/6T. The Poco doesn't work well in the US due to not having all the needed bands. I also have an LG G7 ThinQ which has some support and a SOC that is mainlined. Even being older devices, they still run well enough to be daily dricers, IMO.