I fractured my elbow mountain biking, the tip of my radius. The urgent care doctor gave me a sling and suggested months of immobility. The orthopaedic said to throw away the sling and start exercising the elbow as soon as I could, and prescribed PT. Turns out that was the right move, there are some permanent changes to mobility but it's about 97% what it was before the crash. Immobilizing joints can apparently cause the muscles, tendons, and nerves to seize up and lose significant range of movement permanently.
Something really similar happened to me, I broke my radial head cycling last year.
2 days later I got a call from the doctor telling me to start moving it as much as I could, I asked when I should stop with the sling and he told me yesterday.
Feels kinda reasonable. Human bodies cannot possibly have eveolved to require 6 months of rest to fix. All those humans would have died out thousands of years ago.