Matt Levine does some analysis here: https://www.bloomberg.com/opinion/articles/2020-02-19/the-fi...
Personal opinion, not a lawyer, not your lawyer, is that the further into the global pandemic we were when executing an agreement, the less wiggle room you might have. Again, talk to your lawyer; that's what they get paid for.
The first area where I'm seeing widespread uses of force majeure clauses is the cancellation of large events, conferences etc with limited or compensation for the cancellations. And again, while this hurts some people a lot, this is mostly a good thing, because we do want to give the organizers the ability to break their commitments and cancel the conference with much smaller consequences (to them) than an ordinary cancellation would have; we don't want the organizers to be pressured to hold the event at all costs.