"Save online" doesn't work
As of today MuseScore.com can deal with 3.0 scores.
Currently in Beta "Save online" is disabled, but in the develpment builds the -e option enables it.
Doing that and trying to use "Save online" then though hangs at the Login screen and in the debug output (of a self-built from latest master, using Qt5.12) I see
Warning: QSslSocket::connectToHostEncrypted: TLS initialization failed (:0, ). In the past I got much furter with this, only the upload itself failed (as at that time musescore.com didn't accept 3.0 scores) so I assume this is an issue that needs to get looked at urgently, before enabling "Save online".
Wild guess: Could this be due to TLS 1.0 a) still being used on musscore.com and b) not being supported in Qt 5.12 as being obsolete/insecure? (Would need to try with a Qt 5.9 build, like the current development ones)