Hi,
Thank you for writing to Microsoft Community Forums.
I do understand how frustrating it could be when the features are not working as they are supposed to work. We would like to know the troubleshooting steps that you have performed so that we can eliminate the recursion of the steps.
However, as you have mentioned that Focus Assist gets re-enabled automatically after disabling it. This issue may be due to a profile corruption. Hence, in order to eliminate possibilities, I would suggest you to create a new user account, disable Focus Assist and check if the issue persists. Follow the steps from the article Create a local user or administrator account in Windows 10 to create a new user account.
Hope it helps.
Please reply with the status of the issue, we will be glad to help you further.
Nikhar Khare
Microsoft Community - Moderator