Does pmr slow down healing?

If you are still taking Prednisone, it is more likely that Prednisone is delaying the healing process.
https://www.americanjournalofsurgery.com/article/S0002-9610(13)00221-3/abstract#:~:text=Conclusions,wound%20healing%20in%20susceptible%20individuals.

Sorry to hear that your recovery is not going well after removing the ankle hardware and the wound is not healing. I'm not a doctor but I'm thinking if your PMR is in remission, it's out of the picture for affecting the wound healing. While you wait for members to respond you might want to scan through the comments by other members on "hardware removal surgery not healing" - https://connect.mayoclinic.org/search/comments/?search=hardware%20removal%20surgery%20+not%20healing.

Here's some information from NIH on Impaired Wound Healing that might be helpful - https://www.ncbi.nlm.nih.gov/books/NBK482254/.

You mentioned your doctor is at a loss. Have you thought about seeking help at a wound clinic or getting a referral from your doctor to a specialist?

While I was on prednisone for my pmr I got a nasty laceration on the back of my lower calf. I had 12 stitches and it did not heal very well. I ended up at the hospital wound care center. After my first appointment, I walked out of there with such a sense of relief that it was going to heal. They cleaned it and used Xeroform guaze dressing. I got the best care there. I used that dressing for probably a month and it healed nicely. I would echo John's suggestion about a wound care clinic for an opinion on what would help.