I have just replaced a S10 with a Note 20 Ultra and have had the same issue on both devices. I would like to use the standard Samsung Messages app but I do not receive messages from two of my sons. They both use Pixel devices and are using Google's Messages app. They receive my messages to them, but If I am using the Samsung app I get nothing back. Any ideas?
I have the same problem. Works fine with Google Messages, but when switching to Samsung Messages on my supported T-Mobile Note20 Ultra 5G it can only send messages via RCS. Incoming SMS/MMS is fine but incoming RCS doesn't come through. I suspect it's encryption related. RCS message sent from Google Messages can't be decrypted by Samsung Messages. After sending numerous messages from another phone with Google Messages and Chat Features Enabled, I finally received this message: "Encrypted message. Learn more https://support.google.com/messages?p=messages_e2ee CnYIARJyMwohBTJzWe+GYpkb186lEzdEkeVqS/v2D4jzylUuvp+lafg+EB4YAyJAW7xtlBfx+RKg oiKa7+sL3JwS8FskmkQRnm7k8D6yioVCUguhd8rYBi/ntwbom3doKsbfLABhRIUdv+56tdFQSFFV +E9Z416LEiQ3MzI1ZDM4My1kMWI4LTQ1MzUtYTM3Yy1lZWJmYzg1NGI5Mjc="
Also, despite getting the "blue dot" appearing next to my RCS chats, I don't have the "advanced messaging" option in the "Chat Features" menu on my Samsung Messages app as it appears on other phones. Though I've seen many posts and Youtube videos showing this feature working flawlessly on the S20 and S20 Ultra phones, I have yet to actually see it in action with my own eyes on a Note20 Ultra. I contacted Samsung, who informed me that RCS was supported on the S20 line but not the Note20 line, which just infuriated me because I somehow naively expected the flagship phone in the lineup to at least have the features of the cheaper phones. However I've contacted T-Mobile and they assure me that RCS IS supported in the Samsung Messages app on the Note20 Ultra, but they also were not able to get it to work.
My normal solution would just be to use Google Messages, since it works fine, but I now have a Galaxy Watch 3 which doesn't have a Google Messages app available, and texting is hampered by not using the Samsung Messages app as the default messenger on the paired phone. So I filed an FCC complaint against my carrier. I suggest you all do the same. It takes a few minutes and costs nothing. Maybe if they receive enough of them they'll get on Samsung to fix this issue. Just Google "FCC Complaint" and follow the prompts.