I have been running a LineageOS and MicroG combo on an old Razer Phone 2 for about 2 1/2 years now. Whilst it is not GrapheneOS, it still is a custom ROM regardless.

Most of the usual apps worked with microG, and since GrapheneOS outright implements the real Google Services - albeit heavily sandboxed and tucked away - this should mean that most to all apps should work "just fine".

Just get used to:

- Having more than one App Store. Google Play and F-Droid apps, and possibly Obtanium for anything you need much faster (albeit slightly manual) updates for.

- There will be cases where things are just odd. For instance, I use Organic Maps for navigation and sometimes, while walking, my little dot on the map will just go speeeeeeeeeeeeeeeeeeeen XD. There might be a quirk here and there. But with a tiny bit of patience and a little online-searching-fu, you should be easily able to handle most to all things! And hey, there's that asknostr hashtag ;)

I have had a very amazing experience. Since my Banking app didn't like the information that my phone provided to it, I had to also root it, to then install new system properties AND a module to hide the fact that it was rooted. xD Best-case scenario, you don't need that.

#GrapheneOS is awesome and iirc, there is one of their devs strutting around somewhere here on Nostr. o.o