I've been trying to move an obb file into an obb folder, but it wont let me with the graphene files and other file managers can't even see it. Is there a way to use ADB or some other way to just temporarily gain access and lock it up again?
It isn't Grapheneos specific, it is related to the latest version of Android. If you want to find more, just use your preferable search engine and look it up.
This topic also has been already discussed here. Do not be afraid to use search functionality.