I've temporarily fixed the problem by rolling back one of the Windows updates (KB4601319).
In detail:
Uninstall the latest Windows Update:
* Start > Settings > Update & Security > Windows Update > View update history > Uninstall updates.
* Click on the Date Modified column to sort by the date. For me, at the time, the update was listed as "Security Update for Microsoft Windows (KB4601319)".
In
Start > Settings > Update & Security > Windows Update >
View update history - the relevant update was listed as "2021-02 Cumulative Update for
Windows 10 Version 20h2 for x64-based Systems (KB4601319)" (and
strangely remains listed there even after uninstall).
* Select the update; Click on [Uninstall]
* Restart Windows when prompted.
I've also temporarily paused Windows Automatic updates:
*
Start > Settings > Update & Security > Windows Update > Advanced Options > Pause Updates > Pause until [Some future date not more than 35 days ahead].
Now MLO starts up; as does any Microsoft Management Console
(e.g. Right Click on Start button > Computer Management); as does Visual Studio Code (which previously was also failing to start up, although not previously mentioned).
In short this bug appears to be really on the Microsoft side rather than the MLO side.