hi & welcome! i am a chronic ankle sprainer (when i don't keep up w my exercises). in fact i sprained my ankle in late may. usually cycling itself is great for loosening up stiff ankles as you can go thru a good range of motion without putting weight down on it. it works for me & it's always the exercise (on a stationary bike) that my PTs recommend.

give it a try, starting slowly. good luck.