Signal groups?.... Oh! That's why people wanted usernames.

No. Signal is for people I know.

To me, signal is for friends. Not huge, unknown groups.

Like facebook but they fucked it up. In the early days it was nice to chat with friends.

Some were posted here:

!signalgroups@moist.catsweat.com

I'm in some matrix group chats, but since usernames were added it wouldn't be strange in signal either. But I always mute all groupchats, and read them later.

None. Never.

Matrix is better for an alternative to those Telegram groups that are basically modern IRC.

I'm not on Signal because Signal thinks you should only be able to create an account on an android or ios device so I respect their wishes and don't create one.

Although feeling the same as the other commenters, I gave it benefit of doubt. Using it for 2 groups, Openstreetmap and CoMaps. It works more or less.