I was able to enter the Realm just now. So no longer an issue.
I've had the same issue on the Android version accessing realms after 1.16.100. I thought it could be the texture pack, so I deactivated the pack. But that did not resolve it. I'm not sure what to upload to help in reproducing the issue. Let me know what information might be helpful.
I opened MCPE-107748 which is linked here now. I wanted to report that I am able to connect to Realms now.