Yeah, this sucks! (Excuse my language!)
Hopefully the GrapheneOS developers can find another phone manufacturer that has all the security features a Google phone had, (like the Titan M2, etc, MTE, etc), but I guess it will prove more difficult than "just" porting it, sigh...
Donating to GrapheneOS is always a good idea, (I do that once a year) but it is still alot of extra work regardless, hopefully they can find some more awesome developers next to the fantastic devs they already have.