This patch is, essentially, a rollback of the security features added in early April 2019.
These features were intended to prevent malevolent players from hacking into the game and cheating while playing online. Unfortunately, the changes required have interfered with the game's matchmaking and network systems, with the result that most players haven't been able to play online games at all.
This patch disables the game's security features, rendering it again playable online and fully restoring its functionality.
This also means that the game is, once again, exposed to hacking. The only option currently open to honest players is not to play against random online players who appear to have an unfair advantage. For me, the only other option was leaving the game unhackable but unplayable.
I am deeply sorry for the prolonged loss of functionality and for the long time it took me to recognize and fix the problem. Please accept my sincere apologies.