This virus is wild and it sucks being stuck at home and not being able to train at a gym. I'm probably not going to provide specific routines because everyone and their dog has been posting them on instagram so they're already out there.
Basically what I wanted to say, is don't get discouraged or give up on building muscle if you're stuck at home. There's a lot of concepts and tactics you can apply to keep gaining and at the very least, retain the muscle you do have.
So before we get into training tactics, force yourself to maintain your gym prep routine. So get dressed like you're going to the gym, put some music on, and take your preworkout. Some guys are even finding success with driving around the block or a walk to get out of the house while their preworkout kicks in and then returning to hit the workout. This will do wonders for you gym mentality.
You can get just about everything done with a couple dumbbells and some resistance bands. Honestly, even if you just had resistance bands you could still do everything.
You can basically keep your regular split going, it's very doable to do a PPL split or body part bro split. This is also a great time to switch to a full body split three times a week, like Monday/Wednesday/Friday.
So down to the important training concepts. Really focus on time under tension aka TUT. This means going slow and putting an emphasis on the negative/eccentric aka lowering portion of each rep. This is great if you don't have a ton of weight. You'll put a lot more stress on the muscle and essentially get a lot more out of doing less.
You can combine the above method with pre-fatigue or pre-exhaustion. So lets say it's leg day and you have some dumbbells and resistance bands. Get set up on a chair and do a couple sets of resistance band leg curls and extensions. Go crazy slow and hold those contractions. Then get into your dumbbell squats or lunges and also slow the reps down there.
Another concept that I think is going to serve you well not only this time, but also when you get back into the gym, is maximum fiber recruitment. Not sure if that's a real term but I'll explain. This ideally works best with bands. You want to take a movement, and pre-fatigue the muscle with an isometric hold and flex at the movements peak contraction.
So for bicep curls, you'd get some bands and flex hard and hold a curl at about 90 degrees, where there's the most stress. Hold it for 20-30 seconds and then get into your slow weighted curls. Expect your arms to explode, you're welcome. You can apply this to all other muscle groups and movements as well.