Possibly, on both counts. I know the Guardian and BBC News style guides use that convention.
Yet there’s this regarding the AP Style Guide:
https://grammarmill.com/ap-style-rule-for-acronyms/
It mentions odd rules like “if an acronym is longer than 5 characters” and such.
Either way, my money’s on an internal style guide that Microsoft (in OP’s example) requires its staff to use.
This is pretty close to how I did it.
The “one or the other” thing is a fallacy. You have just one, but they’re clearly happy installing stuff like WA - so tell them to install another app. It’s not like they have to switch.
If they subsequently come to realise the value of Signal in time, all the better.