Muscle Loss

High protein diet, and any exercise is better than no exercise.

Honestly, I dont see how youd lose muscle unless you pretty much stopped training completely. I can go 2-3x a week and keep everything so long as I eat enough. Are you sure you're losing real muscle and it's not just intramuscular water/glycogen etc.?

If you're still WFH, the only equipment you really need is a set of dumbbells for curls/bent-over rows. So many exercises can be done in a timely manner without equipment or with dumbells. 

You should focus on a push/pull workout split (ideally 2x each throughout the week, so 4 workouts in general). Each workout should take you max ~45 mins at home. You can shorten it if you don't have that much time. This workout volume also varies depending on how strong you are to begin with. I'm going to assume you're mid-level. 

Push

Chest: 70x regular pushups, 60x decline (put your legs on an elevated surface, ideally 6-12 inches off the ground). 3 sets of lateral raises with dumbbells until failure. 2 sets of shoulder press (sit in a chair and lift up weights). 2 sets of tricep extensions until failure. 

Pull

Biceps: 6 sets of curls (3 normal sets, 3 sets where you sit backwards on a chair as if your hands are very close to the ground to begin with.) Focus on form and hold the weight for extra seconds once you feel a strong burn. Back: 4 sets of bent over rows with dumbbells. 2 sets of "snow angels" (essentially lay on the ground and try to lift your back up with your arms)

It's all about maintaining when you're an analyst and not gaining the analyst 15 (or 50 I've seen). Eat salads for lunch, low carb dinners. I played football in college so it was hard to adjust to not lifting everyday. I now lift 2-3 times a week and run at least a mile or two everyday to maintain my physique. Everyone can run for at least 10 minutes a day to stay the right size, along with eating healthy 

If you get stronger on the main compound lifts while maintaining the same weight, you will gain muscle guaranteed. Try to stick to a few core lifts and maintain or improve your strength on them. These could be barbell (or dumbbell) flat (or incline) bench press, weighted dips/pullups, barbell rows, deadlifts, squats, barbell rows, standing overhead press etc. Throw in some isolation work if you can, but try to hit 2-3 main compound lifts each workout and gain strength on them. You really don't need to be in the gym more than 2-3 days a week if you do a full body routine. If you gain strength, sleep right, and eat right, you will gain muscle or maintain it. You don't need a shit ton of volume to grow as a natty if you're training close to failure and gaining strength. If you keep your workouts focused mainly on compound lifts, you should be able to get valuable workouts in a reasonable time. You might have to throw out some of the fluff and pump iso work, but that doesn't contribute to much of your growth anyways.

It's very simple: find time to get a 45min - 1hr workout in and crush food 3-5x a day(healthier unless you're tryna put on the analyst 15/bulk). Sprinkle in as much sleep as you can and you will grow.

Source: former college athlete who used to be a "unit"

get a 20kg weighted vest and do loads of squats, pushups, upside down push ups against the wall and dips at home if you have no time to go to gym. 

The best advice anyone can give that nobody has touched on here- make it a priority. Priorities get done, simply move it up the list of priorities and don't have it as an after thought

I think one of my balls became smaller and my overall length decreased like 0.14" since college, might just be natural aging though

Offer to get the pitchbooks and use the stairs for workout.