Did you commit your changes? IIRC Alpine for Raspi is installed in diskless mode by default and is immutable.lbu cmmit

I tried it once a year ago, message was delayed. Immediately switched to another App (QKSMS).

What? SMS is a proven standard that works reliably. Why do we need to replace that? I tried RCS twice, in both cases the other end did not receive my message or at a later time. Even if SMS needed replacement, RCS is not it.