Would this annoy you? 25 squats every hour

No, that's just you 😂

It's a shame he doesn't want to support you improve your fitness.

I often do things like do some squats while I'm waiting for the kettle or microwave, stand on one leg when I'm brushing my teeth to practice my balance. My DH has never made a comment or given me his opinion on this. I wouldn't take too kindly if he did. What does it matter if you do some squats while waiting for the kettle to boil?

Well done for doing something for your fitness.
My confession is that my DH has just discovered yoga, and now I come across him unexpectedly in the lounge or the kitchen, contorted into some unyoga-like positions, when I just want to catch up on Corrie or stick the kettle on. It's unnerving 😂
But I'm glad he's doing it so while I might snigger (can't always stop myself bless him he does look funny sometimes) I won't ask him to stop or do it somewhere else.
Now about those squats. Why 25? And why just squats?
Have you thought about trying couchto5k? If you are jogging for 10 minutes you will probably do it easily. Look for the NHS health unlocked website, there's an app you can download.
On the couchto5k section you'll find a lovely group of people who will support you, give advice, and point you in the right direction
There's also a sister site called strength&flex (still part of NHS unlocked) that will give you lots of different exercises and stretches. There will be guidance about how many sets of each exercise, and how many repetitions.
There's a lot of crossover between the sites.

The OP says very clearly that he hasn't asked her to stop doing it, so I think this is a bit of a stretch.

Personally, I'd find it a bit irritating if someone started doing squats every hour. It strikes me as seeming a bit performative (although obviously it's not intended to be), and it's the kind of thing you can sort of see happening out of the corner of your eye when you're trying to concentrate on other things.

I would be pleased my partner was improving his fitness a bit, and I probably wouldn't say anything, but I'd secretly be thinking 'If I have to watch him do those bloody squats one more time I'm going to go silently insane'.

Every hour is quite a lot and I find it quite annoying in general when people are fidgety and keep getting up and faffing about, so hourly squats would probably irk me, on the quiet.

OP, YANBU for doing them but he is also YANBU for finding it mildly irritating.

Yanbu. He doesn’t want you improving yourself! It’s a tale as old as time.

I’ve seen this type of sabotage so many times. Next he’ll be bringing you calorie-laden chocolates home.