Hey good_guy, if you are like most of us, you had to take a 12-15 month break from the gym. I was happy to be able to get in after 13 months (April, although the locker room and showers were closed until late May). I am hoping you've gotten back into the regime - it takes more to begin a workout routine but, once it becomes a habit, it's easier to maintain. And I can now answer your questions about how long it takes to see and feel a difference.
For me, I had noticed a drop in mood and energy before I got back in - could have been the lack of rigorous gym weight-lifting and workouts but it also could have been the long pull back from socializing and normal life. While I maintained good exercise on the farm, I could see and feel a reduction in my muscle mass and strength.
Now that it's been more than two months back in workouts, I definitely notice a difference. I had to initially drop as much as 30% of the weights in my regime (3 different days of workouts each week). Now I range from 80-100% of my pre-COVID free and machine weights and about 60% of my rigorous core workouts. My mood is solidly back up, and I have bonded even more to workout buddies who are also scrambling to get back into shape. As far as looks go, I am now nicely defined after just a couple of months and, as a 63 year old, it's great getting compliments again from guys who could be my sons (or even grandsons!). While my libido didn't suffer too badly during COVID (though there was FAR more jacking off than hooking up), I feel hornier now, and my sexual appetite is compelling. I even started getting a chubby while taking the last photo in the locker room <grin>!
If you haven't yet gotten back into the gym, it's really great to do so now that everyone else is just resuming - you will have much more in common with everyone else there, and it's more likely you can give, and get, encouragement form others. My best to you!