I can almost guarantee that the issue is a carrier issue, I use RCS on an iphone and it works out of the box, and I have all the things you listed for troubleshooting.
+1 for this being my experience. Used RCS on a Pixel 6a and a Pixel 8 before switching to an iPhone. As soon as my carrier got approved by Apple (or whatever the hell that process was), RCS just worked out of the box with my (increasingly few) Android friends. I was actually surprised by how smooth it was, once it was actually available from Apple.
