Hi, hope you're doing well. I’m Ian, an Independent Advisor and Microsoft user like you.
As of now, there's no option to turn it off by default.
I would suggest to submit feedback to the development team in the link below so that they can add this in the future releases.
https://word.uservoice.com/forums/304924-word-f...
As for the behavior of the markup, as long as there are tracked changes or comments in a Word document, it will show them for you, as you (re-)open the document. This is a privacy option. You can turn it off in Trust Center Settings, go to File > Options > Trust Center > Trust Center Settings > Privacy Options thenclear the option to "Make hidden markup visible when opening or saving". Take note that this setting is local to your machine. You can't control what other people see if you send them the document. To permanently get rid of the markup, accept (or reject) all changes and delete comments.
This is a user-to-user support forum and I am a fellow user.
I hope this helps, but please let me know if you need anything else.