My son is holding this over my head and wants to move with his dad?

He's not "blackmailing" you. You've said that 4 adults  in that apartment is cramped.  He's a man and he recognizes that it's time to go, but he's willing to stay to please YOU if things can be improved.  

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Encourage him to go as soon as he's ready. Men relate to our fathers differently than with our mothers, so you dunno if they're close or not.  You know that he's close enough to his father to believe that they can get along in the same house. 

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He's a man--he's been shaving his face for 5 years. He'll be OK with his father. If not, he can move out of his house. 

Nancy, in YOUR mind, you and your younger son are close.  In his mind, he's looking for an excuse to leave and he's using emotional blackmail on you.  He knows that you think of him as your baby (your youngest), and you want to keep him close to you.  For that reason, he's pressuring you to do what he wants, with little or no regard to the reality of the present situation.  So he's losing some sleep--does he not realize that with this COVID situation, EVERYONE is under pressure, losing sleep, and on edge?  Trust me, your location has little or nothing to do with his thinking.  Obviously, he's been spoiled and used to getting his way for most or all of his life.  Now he's using that to make you feel anxious, and he's manipulating you (which I'm sure he's done a lot of in the past).  What you need to do is do the right thing for you and your other two children.  Don't they count for something?  Let the spoiled child go with his father to Idaho.  I can tell you that he has no idea what he will be getting into.  I don't know where you live, but there are more people in the city of Dallas (where I am) than there are in the entire state of Idaho.  The scenery is okay, but it is unbelievably cold from September to May.  It begins to snow very early, and it can snow until April.  The job market is very spotty, because there aren't that many jobs to choose from.  Idaho people are opinionated and stand-offish.  Your son won't be able to manipulate anyone if he moves there.  He will be begging to come back to his mommy.    The best thing you can do for him is to make him grow up.  When he comes whining back and wanting to move in with you, you need to tell him that he made his decision to leave, and you and his siblings are fine with that.  Now he has to figure out what he wants to do with himself in Idaho, since he was determined to live there.  The culture shock will be the best lesson of his life.

Your son is not a child, so should know better.

His behaviour suggests that he does not think of you as being close.  Getting a job in the current situation may not be easy.......but at age 19 he was unemployed before this situation.  Have you, unwiittingly, contributed to his non working? Are you trying to keep him ‘tied to your apron strings’?    He is at an age where the two of you should be able to sit and talk sensibly.  

If, however, he insists on moving with his father, he may need to learn the hard way that life does not owe him a living 

Your son is an adult and you need to adopt the idea that he should be starting to separate himself from both you and your ex at this point in life. You seem to view this as some kind of punishment when really it's the so called "circle of life". Make your plans as you can but if he wants to try living in Idaho let him go do that and don't be nasty about it. The best way to make sure he doesn't ever want to live with or near you again is to make this into a battle. 

Offer to help him pack for his move to Idaho.  Ask him if he needs another suitcase.

That's the only way to deal with an ultimatum from anyone, including immediate family.  Whatever you're being threatened with, accept the worst-case scenario no matter how difficult it is.  There's no other way.

When you were six and told your mom you'd run away from home if she didn't buy that certain thing (doesn't matter what thing), what did Mom say?  She told you where the door is, didn't she?  And that's what you need to do.

He's 19, a legal adult.  He can live wherever he wants to live.  I don't understand the "holding over your head" part and, by the way, you don't sound terribly close.

i would just let him do what he wants

Tell him goodbye, and this is the best advice I can give to you. I understand you want to live in an apartment, and your son's father wants to live in a house.

Your son is looking out, for his own interest, so that's pretty good. He knows that if he were to move with his father then his lifestyle would change.

You said "We live in a building that can get kind of loud and it is on a busy street. My son says he loses sleep here and he complains about a lot of things here where we live."

Well if he were to move with his father then just try to imagine the amazing sleep he is going to get over there.

Regarding myself I plan on moving, but I don't have a date yet regarding when I will be moving. I am not sure yet if I will be moving to an apartment, or my own home that I would be buying, or maybe both.

Well I am still trying to plan out where I will be moving to. Regarding the covid-19 well this won't stop me from moving, and it should not stop you either.

Call his bluff. Tell him you'll miss him, but you'll understand if he wants to go to his father's (even if you won't).  Don't let him use emotional blackmail to get you to do something that isn't right for you.  He's 19. He can live wherever he chooses.

Tell him if he wants to that’s fine just assure him that you love him and he’s welcome to come anytime to see you.  If you try to stop them I will just make them resent you, trust me my mother did the same thing.