Incorrect default shortcuts for 'Zoom in' and 'Add tied note to chord'
The default shortcut for 'Zoom in' is Ctrl++. Pressing Ctrl+Shift+= in the score view doesn't zoom the score in.
Google Chrome allows both Ctrl+Shift+= and Ctrl+= for zooming in, so I think these should both be the defaults in Musescore.
Starting from 3.5 Alpha, there are now also default shortcuts for the piano roll editor and these have the same issues. For example, 'Zoom in vertical - piano roll editor' should be Ctrl+Shift+=, instead of Ctrl+Shift++.
'Add tied note to chord'
The default shortcut for 'Add tied note to chord' is Alt++. Pressing Alt+Shift+= doesn't work. This should be 1. Alt+= or 2. Alt+Shift+= , depending on the intent of who implemented it. Since the shortcut for 'Tie' is + (Input as Shift+=), it would make sense for it to be option 2.
The issue here seems to be the definition of the shortcuts, but there might also be an underlying problem. The shortcut for 'Tie' works and is defined as +. This requires two keypresses, but is defined as a single +. However, adding a modifier before this plus makes a shortcut not work, like in the case of 'Add tied note to chord'.
Also, when trying to change a shortcut inside Musescore to for example Alt+Shift+=, results in Alt++, which as I've discussed doesn't work. The only way I can see to use that specific key combination is by editing the shortcuts.xml file manually.
Some other examples when trying to assign shortcuts (on the US-International keyboard layout):
Pressing Ctrl+Alt+5 results in Ctrl+Alt+€.
Pressing Ctrl+Alt+= results in Ctrl+Alt+×.
This is the behaviour in Musescore 3.4.2, 3.5 Alpha and the current latest master 188.8.131.5273, revision: 4650a2f
OS: OS: Windows 10 (10.0), Arch.: x86_64