I did daily planks until I fell on my ankle. After that, it wouldn’t hold me. I finally tried it last week and was able to be on the ankle and toes on that foot for 30 seconds. It’s not much but it’s a start. I credit planks for keeping me so strong prior to the ankle. The bone loss didn’t come along until after the ankle.
You’re just gonna have to cut it off and let it grow back.
It's true, weight-bearing exercises help prevent bone loss.
Have you tried a youtube search for exercises you can do which don't require the ankle to bear weight (e.g. some machines or resistance bands, where you *pull* with the leg rather than hold things up)?