UUPSUpgradeable Vulnerability Post-mortem

If you are thinking about major changes, perhaps you may want to consider adding protection on who can run initialize.
IMHO, leaving the possibility of having contracts that might be initialized by anyone even when they are implementation contracts it's a potential threat. Let's say someone initializes and hijacks an implementation contract deployed by a trusted address, and with social hacking methods tries to make people interact with that contract instead of the Proxy.

Following the same patch you did for 4.3.2, you can add an immutable variable registering the contract's creator address.

 address private immutable __self = address(this);                                                                    
+address private immutable __creator = msg.sender; 

And then put a validation on initialize function that has to be called either from the proxy or from __creator.