Solved! Go to Solution.
Quick question, your S20 was it also unlocked or did you buy it through the carrier? I noticed my old S10+ which I had bought through AT&T also had the chat settings (RCS) feature. But now with the S21 Ultra which I bought unlocked directly from Samsung, this feature is not there. Doesn't really bother me since I use Google Messages anyway, but I have noticed that this feature is no available on the S21 Ultra for me.
Try going into the play store and install carrier services, see if that works.
Hope that works for you, if it doesn't give Google Messages a try. Me personally I prefer that over the Samsung Messages from the looks. The only thing that is missing with that, is the scheduled messaging. But everything else works perfect.