protonuser2 UPDATE: This issue is related to running the app on the non-owner profile.
Behavior is as expected on the owner profile.
I wonder what setting/bug caused me to have so much SMS app related issues on the non-owner profile.
Thanks for looking into this further. There are reliability issues with sending and receiving SMS issues in secondary user profiles.
It's generally not possible to send and receive SMS in secondary user profiles with third party apps. As far as I know it affects all third party SMS apps: this is not something specific to QKSMS.
This is not a GrapheneOS specific issue, but an upstream issue from AOSP, and I believe it also affects users on stock Pixel OS.
If you want to send and receive SMS in your secondary user profile, you'll need to use the default Messenger app, that works fine. I have also heard that Google Messages might work, but haven't tried it.
In the owner profile you can stick with your preferred SMS app, and it'll work fine.