Hello I install zangi app it's for chat, I don't received notification when I send the message from other phone all notifications is enabled what is possible but it's not working, only then when I open app I received notification and message.
On phone with Android huawei I received message with no problems
Grapheneos - - > simple android ( I got message and notification)
simple android-->Grapheneos (only then I open app I got notification and message)
If it's possible you can test on you maybe
P. S. I dont use Google services and I don't whant to install.