I recently heard about Databag. It's a decentralized and federated end to end encrypted messaging service. It could help with the issue. As long as you have or know someone who could run a node on some server space or even a rasberry pi
Afaik there is a build flag in the source code for Signal not to share your number in group chats but that has been there for quite some time. The Signal team really takes its time on this one…
I did that. I lost the burner number after it got rotated. Months later, I lost my Signal account when someone apparently used the number to setup an account on Signal.