A happy ending update to my situation...
I completed a trip (week long flight basic economy on Delta with my FB account on it. $400 for good Saturday-Saturday flights) and the miles posted within 24h on my KLM account after flight. I just got off the phone with the original FB number in my original post. Quickly got talking to agent. Gave her my FB account number and explained in 2 sentence what I'm looking for. She confirmed my flight credit to Seattle, and in a minute, my expired miles is in my account again.

I further asked her if I was lucky and she said this was a policy for customers with expired miles during 3 years of COVID lockdown. It wasn't just for me. I did not ask her when this "policy" ends...

Sorry for not being as "informed" as I used to be, but what do I have to do keep my FB miles from expiring again? :-)
1. Only flying butt-in-seat?
2. credit card spending?
3. Spending at least some miles with a flight or magazine subscription or donation?
4. No way to keep all my miles for ever like some Japanese/Korean airlines...gone after x years?