defaultSymbol and fa library versions.

[Richard238]

defaultSymbol links to https://fontawesome.io/icons/ which gives page not found error.
Also, latest MM update (Apr '22) changes fa library version, possibly causing icons to no longer load.
e.g., fa-calendar-check-o (fa v4) no longer works.
Backward compatibility ought to be implemented to accommodate older fa library versions.
Instructions need to be fa library version specific.

[MichMich]

Please send a PR with the suggested documentation modification.

[khassel]

defaultSymbol links to https://fontawesome.io/icons/ which gives page not found error.

which default symbols do you mean, AFAIS there are 2 mentioned concerning calendar, one in this documentation (calendar) and one in the config.js.sample (calendar-check). Both are still working.

Also, latest MM update (Apr '22) changes fa library version, possibly causing icons to no longer load.
e.g., fa-calendar-check-o (fa v4) no longer works.

updating these library is a normal process, no one can rely on the icons provided by fontawesome to exist or are free after they update their library. Where is fa-calendar-check-o mentioned in mm documentation or mm core? You are responsible for icons you are using, if they don't work anymore check if they are still availably/free, otherwise use a different one ...