I have successfully installed GrapheneOS on a Pixel 3 and set up a second user profile. This is my first venture into the world of Android (after a good deal of reading). I thank those responsible not only for providing the OS but for making it a practical proposition for those without great knowledge of the Android system.
To my problem: I have installed Signal on the second profile and successfully imported my messagebase from a previous phone. On that device I used it for both Signal and SMS, which I have attempted to reproduce. Signal appears to be working but I cannot get it to function for SMS.
Android Settings > Apps > Signal > SMS app shows Yes.
Signal > Settings > Chats > SMS and MMS > Use as default SMS app shows 'Disabled'.
Attempts to send an SMS fail.
I have stated my lack of knowlege and will be happy to be corrected but I suspect that the problem might lie with the SMS utility in the first profile.
I will be pleased to receive any comments.