I'm gonna go ahead and disagree with what most other folks are saying...not every non-FTF transaction on Armslist is a scam.
The biggest red flag is that they said they CANNOT do a FTF sale...how is that possible even with COVID? Absolutely sounds scammy!
In your case, I would be extremely cautious. Ask for his FFL's information, then call the FFL and confirm that they'll be sending it out. Call the seller and have a conversation. Get a feel for who they are. Don't be afraid to ask prying questions about exactly what they plan to do, and why. After all, they're asking you for money up front.
If everything checks out, the FFL says "Yep, Joe is a good dude, we'll be taking care of shipping the firearm." And then you have a pleasant 5min phone conversation with Joe about guns and his last hunting trip, you'll probably be fine. If you get a weird feeling during any part of the deal, and the seller can't or won't do anything to fix it, just back out. No harm no foul.
I've sold a couple guns on armslist this way. Guy emailed asking if I would ship, I responded with my phone number and we came to an agreement over the phone after bs-ing and feeling eachother out.
Good luck!