I hope it's comforting to learn this subject has been studied for well over a decade, and the results provide a clear answer:
We lose progress at a significantly slower pace than most think—especially when it comes to muscle mass and sheer strength.
In fact, even if you have done absolutely nothing for the last three weeks, you still haven't lost any muscle. Pretty dope in my opinion.
So, let's say you were hitting the gym 5 to 6 days per week before COVID-19 jumped on the scene...
Even if you reduce your amount of training to 2-4 days per week doing at-home workouts, you'll be able to prolong any muscle catabolism (burning of muscle for fuel) for months.