My dad is 83 and is spending 85% of his time in his armchair watching TV and sleeping. Is there anything we can do?

Sorry, don't mean to compare him to an old cat,,, but that is where I am heading. Let him lie around, wake up and look around. ,meow for a snack, and a treat. Let him be... HE IS ALLOWED.... It is OKAY... keep him happy. Know that you are trying to keep him happy..
It will be okay.. feed him what he wants to eat, let him rest his eyes, and if he wants anything more,,,I see weirdly a vodka tonic... (?) why... no reason.
keep him happy, make video conferences to his doctor. keep in touch with his medical team and know you are doing everything as right as you can do.
play games, cards, darts, etc...just keep it fun a nd light

It could simply be what he wants to do. Aging and it’s progression are different for everyone.

Hmmm, I'm not quite certain what you are expecting him to do. He's had a stroke so I imagine there may be some physical, as well as cognitive, decline. He's catheterized and has Parkinson's. We are in the middle of a pandemic where people have been encouraged to stay home and away from others for their own safety. So he's decided to watch TV. So have I. He well may be depressed (aren't we all at this point?) and may benefit from a mild antidepressent but he may just be responding appropriately to his situation. Does he participate in conversations when if he has guests? Does he talk on the phone when called and respond with more than monosyllables? Does he refuse to do appropriate activities that he used to enjoy? My dad is much older than 83 but he slowly stopped being as interested in things he previously enjoyed as he aged. He was very active in community bands and both played in and attended many concerts. He always wanted to attend musical activities at his assisted living. Over time he didn't go as often, he'd make the decision that his favorite chair in the sun was preferable to sitting around on an uncomfortable chair at the musical event. What makes you happy can change, especially when you have declining abilities. So, have him checked for depression but don't worry about it too very much as it doesn't seem like in our current situation there are a lot of activities or opportunities to be "on the move."

I agree with Daughterof1930. Sometimes treatment for depression, mild medication if indicated, can make a big difference. Not certain what medications are being taken for Parkinsons? Some can act as depressants. SPEAK with your Dad. Ask him to go for neuro-psyc eval. Tell him that you understand how hard all this is for him.
That will at least be trying to do something. And then, truth told, some elders do not react well to the long slow slide down with loss after loss after loss. There is no upside. With the things he is dealing with it may be the only diversion that relieves him.
Remember, we often talk around our elders instead of too them. Try not to speak to him as though you are forcing change. ASK him. ASK him how he feels, if he has any goals moving forward, if he feels hopeless. Tell him some times mild medications help to form a bridge over tough spots.
Wishing you the best and hoping you will update us.

When my mother had a stroke we watched her personality change. She lost interest in activities and the people around her. She just sat, completely unlike the person we knew. The suggestion of depression made her very upset, but we now know that’s exactly what it was, it’s very common following a stroke, and our family regrets not pushing harder for it to be treated. I hope you’ll get your dad to his doctor and voice your concerns as you have here, being properly treated for depression could make a real difference