Constipated cat has problems eliminating.. how else I can help him?

Sphynx, male, 12+ years, front paws declawed. Health issues: crystals and PU surgery, pancreatitis, constipation. I got him 4 years ago, already declawed and after PU surgery. He is on prescription RC urinary so wet&dry food.

Ever since I got him he seems to have difficulty eliminating, occasionally running around with loud meows and pooping around the place.

The litter (currently tofu based) is gently on his paws and it doesn’t stop him from using litterbox. It’s more as he has to run around to get it out. And sometimes he is very vocal while doing that.

Our regular vet seen him for that, xrays and bloodwork was done but haven’t discovered anything abnormal. They also just got him edema, and previously to that visit another vet commented that “this cat has a lot of poop inside” after looking at his xrays for unrelated issue.

I am giving him 1/8 tsp of miralax and fiber daily. But he still have the episodes. The poop coming out well formed and not dry, but definitely uncomfortable for him.

Is there anything else I can do to make him more comfortable?

Also, he is getting “restless” episodes throughout the day when he is just running around with loud meows.., not always related to popping. I am not sure if those are age or discomfort , but the guy is definitely not as happy as I would love him to be

Any advice would be appreciated