Yes, you are not the only one. A lot of apps have mic problems on the FP3+. Just as an example, have a look at this thread
In my opinion this is clearly a software problem. The mic is working fine in a few other apps and also the test option (by entering *#*#66#*#*) shows that the mics are working.
So this is the good news: For sure this can be fixed by a software update by Fairphone. Let’s hope this will happen very soon!
Yes, that’s the bitter thing: Being in lockdown and having a phone that makes it even more difficult to keep contact with friends and family 