The "Beta" guy makes me laugh.
The issue with iOS 13.3 is specifically related to re-activating iMessage and Facetime. If iMessage is working prior to the upgrade to 13.3, chances are good it will work afterwards too. Should you pull your SIM or turn off iMessage, you won't be able to activate it again. During the attempt you will get weird texts from Fi that you should never see. I am told these texts are as a result of some kind of registration handshake error. In my case, my 11Pro Max worked flawlessly with iMessage for a month prior to 13.3. In fact, I have Verizon in the eSIM and Fi in the physical slot. Both numbers were activated for iMessage. I have tested iMessage activation with Fi on my 11, an XS and an 8 Plus. Same results.
Both Google and Apple are clueless on the errors. I have spoken to level 2 for both. I suspect the "fix" needs to come from Google and not Apple (13.3 still activates just fine with my AT&T and Verizon SIMS in the same phones). It will probably take more people experiencing the problem and complaining/posting before Google wakes up.
Downgrading might be an option, but I have read on other sites that success is hit or miss and you might lose data. I also hate for people to miss out on the latest bug fixes and security updates. Sometimes that is worse.
We all need to keep contacting Google and following up!