To enable ADB on an Amazon Fire Tablet, first activate Developer Options by tapping the "Serial Number" repeatedly. After Developer Options are enabled, find the newly added menu in Device Options ...

And one of the most useful tools for hacking Amazon’s tablets is a free third-party utility called Fire Toolbox. Amazon Fire HD 8 (2020) with Google Play) ...

So folks have been finding ways to hack Fire tablets for almost as long as Amazon has been selling them.