I sometimes get them and sometimes not until I open the Signal app.
I've had this problem on all my Pixel phones running GrapheneOS.
Pixel 7 Pro XL
Pixel 8 Pro XL
And now Pixel 10 Pro XL.
I installed Google Play Services and Play Store first, then Signal.
My phone has both data saving or battery saving disabled.
Both Signal and Google Play Services are allowed to run in the background with unrestricted battery usage.
They are also allowed to use unlimited mobile data.
I have excellent WiFi and mobile reception.
I have even tried with Molly and UnifiedPush with my own server - same result.
When I send a Signal message from my other phone, I see that my phone receive it at once, yet no notification.
(Years ago I also had the same problem with matrix clients, but since I don't use matrix now I don't know if that would also be a problem, but I suspect I would).
My friends running stock Android does now have this problem and on iPhone I never once had this issue.
Either there must be a setting I'm missing or there must be something with the OS.
Any input is appreciated.