Things like that are sourced from the icon theme now.
It can also be force-set in something like the Global Theme by using something like
"/General": {
"compactMode": "true",
"favoritesPortedToKAstats": "true",
"icon": "/usr/share/icons/start-here-manjaro.svg",
In the layouts.js
Between the difference mentioned above, where the Desktop Style no longer mandates such icons, and the status of the icon theme itself - that is what created the lack of the ‘M’.
This can only be fixed via one of the methods mentioned above - so in the case of something like Icons it would need to be a package update - but manjaro no longer provides, ex, Breath Icons, so that wont happen unless a new Manjaro Icons package is created (and installed/selected).
Which then leaves the Global Theme.
A change could be made like shown above - but would still require manjaro to make such an update - and then the users would need to apply that Global Theme again.
On a somewhat related note - manjaro really should update its ‘agnostic’ icons it distributes (/usr/share/icons/manjaro via manjaro-icons). The defaults look bad and oversized on panels etc.
Heres some I posted for someone the other day: