Donkeys and Mules always have the same speed and jump strength. In Java, spawned donkeys/mules have the same speed and jump stat. However, better offspring are possible with the following formula (parent stat + parent stat + random stat)/3. Increasingly difficult, but possible. In Bedrock, donkey/mule stats never change regardless of parent or random stats.

I believe this is a glitch, not an intended difference as it prevents progression through the mechanic of selective breeding.

This does not apply to the health stat. Like wild or spawned donkeys/mules, bred offspring can have varying degrees of health.