My cat is too aggressive to get a checkup

At the last 3-4 visits at the vet my cat is too aggressive to get a proper checkup. The last two were so bad the the vets sent me home since they can't treat him properly. The assistants can't even hold him properly because he starts aggressively kicking and run away unless I hold him, but even then he gets uneasy and squirmy when someone else gets close. I don't know why, because he's never been abused and I think in his earlier years he never had this much of a problem with vets either. I don't know if maybe during covid something happened. During that time I was not allowed into the same room as the vet and I heard my cat scream as he was getting a checkup. The vet still treated him so maybe that's where it started, since he was held down against his will (I assume, I wasn't there).

Today I tried a new vet who was super patient and understanding yet still my cat immedietaly threw a tantrum. The vet before that was also very gentle and for that appointment my cat even got some kind of tranquiliser as a pill and he still was too aggressive and had to be put into some sort of extra bag that barely helped as well.

I was recommended a spray that's supposed to be calming but honestly I doubt it'll work since the pill already didnt work at all except for him sleeping after the appointment.

He's usually not aggressive at all, when he wants to play he doesn't use his claws and he seeks cuddles frequently. He lets me squish him or tease him with no reaction at all (I don't know how to word it but I can basically throw him around and he wouldnt care at all (of course I don't, I'm not actually rough with him (does that make any sense?? ;-;)).

I'm lost because he needs a checkup. He's been having coughing fits, went deaf and started eating less (He's about 8 years now). But again I was sent home today without a real checkup because they couldn't hold him down and of course didn't want to be forceful either so I understand. The only option the doctor gave me was to give my cat anaesthesia, with the risk of not knowing his condition beforehand and the risk of heart failure, which is especially common in mixed breeds. And since I don't know what the problem is, and I do worry it may be surrounding the heart, I'm too scared to risk it.