Vet Opinions on Activity/Exercise Requirements for a Geriatric Cat?

Hello vets!

I have an 18-year-old indoor male cat. He's had chronic kidney disease and hypertension for 2+ years but has been mostly stable with an aggressive diet/meds/fluids regimen. He was up at IRIS stage 4 in their beginning but it's in low-mid stage 3 now. Other things have come up like non-regenerative anemia, hypercalcemia, acidosis, etc., so it's incredible he's still here and happy.

My question is about exercise: Given his very advanced age and medical challenges I have not encouraged extra activities. He's mobile and has no issues with stairs but he mostly just wants to sleep in my lap or snooze under a blanket. He shows little to no interest in toys, cat trees, etc., though I keep trying just in case.

I know he doesn't feel well sometimes and he's happiest just being comfy. He's so old and the medical issues, though currently managed, take such a toll that I'm reluctant to encourage exercise (especially when he shows no interest).

Do you think I am doing him a disservice by making his comfort the priority or should I still encourage him to be more active? All feedback is welcome. Thanks!