As you can see, summon a wither with no AI via commands (/summon wither ~ ~ ~ {NoAI:true}), then exit and re-enter the save. At this point, the orientation of the wither will not change as intended. It rotates in a certain direction, but why would a creature without AI do the act of spinning?
Attack this wither that doesn't have AI. The creature can still be damaged, but the boss bar doesn't change in any way. The boss bar shows that the creature's health has nothing to do with the AI.
Use commands to summon an ender dragon with no AI (/summon ender_dragon ~ ~ ~ {NoAI:true}). This mob cannot be attacked normally by the player and does not display a boss bar. However, TNT can still injure the ender dragon.
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Thank you for your report! Next time, please submit one issue per ticket and use the vanilla launcher. Your F3 debug screen shows that your environment is not 100% vanilla.

The Environment field is supposed to only contain PC details.
Thank you for your report!
We are tracking this issue in MC-74114, MC-84243, and MC-266796, so this ticket is being resolved and linked as a duplicate.
The former two tickets — MC-74114 and MC-84243 — have already been resolved as Works As Intended, which means this is not considered a bug and will not be fixed. Please do not leave a comment on those tickets.
The latter ticket — MC-266796 — is currently resolved as Awaiting Response. Please take a look at the comments section to see what information is currently missing. If you would like to provide the requested information to that ticket, it would be appreciated.
Additionally, your launcher is modified. Please only report issues that you have verified to be present in a vanilla environment, and make use of the search feature to see whether an issue has already been reported.
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