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For some, password fields which refuse to accept a space as a valid character is enough to raise their blood pressure noticeably, they should probably stay away from macOS 10.15.1, politely known as Catalina. Thanks to an issue with certain hotkeys, the letters B, L, M, R and T are also excluded from being used in a password in at least some apps, certainly the Twitter desktop app is included in that list according to The Register.
There is no word yet on when this bug caused by regressive feature will be solved by Apple, so either hold off updating or changing your password for the nonce.
Twitter says a bug in macOS 10.15.1 aka Catalina stops users of the social network's desktop Mac app from entering certain letters in account password fields.