A bit of an AIBU, but hoping to avoid the slating of AIBU.
DH and I have two children, almost 3 and 9 months.
DC1 is generally a really good kid. He has a medical condition that means he doesn't sleep well and is often tired. Even napping in the day at nearly 3, he struggles late afternoon and can be grumpy, occasionally tantrums. He's waiting for surgery to hopefully correct the problem. Other than that, he plays nicely with his toys and loves nothing more than to snuggle with you and be read a pile of books.
He can be a bit toddler-ish of course, takes toys from the younger one, because he sees the cars/trains etc as 'his', which I'm working on correcting.
The youngest is a baby of course, happily plays, wants to be doing whatever DC1 is doing.
My issue is the lack of DH wanting to do anything with them. I see other dads playing with their children, but it's rare that DH does that.
He's working far fewer hours right now - covid affecting his industry, so he's home more than usual.
I'm noticing him be very short/grumpy/snappy with the toddler and if I ask him what the matter is, "he's being annoying" or similar.
If I ask him to watch the kids so I can go upstairs so I can get something done, might (for example) lie on the floor and look like he's playing with DC but as soon as I walk in, he's clearly just put his phone down next to him. Or he will be sat on the sofa scrolling on his phone.
(I appreciate I'm clearly on MN now, but both children are napping).
He's uninvolved in terms of play - doesn't sit down to play with them, doesn't do nursery rhymes, does read granted but if he's in a bad mood, it will be with no expression or interest etc.
The main childrearing tasks he does, he will take the baby upstairs for the afternoon nap and will cuddle baby on the bed upstairs; and while I BF baby at bedtime, he puts toddler to bed (he does story and sits next to him while he falls asleep - rarely a long job due to this medical condition. Of course, he's on his phone.
He's just seemingly uninterested in his children. He'll do practical stuff like collecting from nursery or putting a wash load on for example. He just seems uninvolved emotionally. If he's "watching" them, it's just that. Making sure they're not injuring themselves rather than engaging with them.
He also feels the need to get out somewhere each day, i.e. to get x, y, z from the shop, which he recently referred to as "getting away from us for a bit" then tried to say that it's the same as me having a soak in the bath after the children are asleep 
I'm at a bit of a loss really how to get him a) involved and b) wanting to be involved.
If he interacts in an age appropriate way, it takes me by surprise it's that unusual.
What can I do to fix this? It just makes me sad that he's bored by our children when DC1 is so kind, caring, loving, funny and clever although like any toddler, he has his moments and DC2 is already loving, inquisitive, energetic.
I do wonder if I'm going to end up on my own with them.
Any thoughts please, hive mind?