Okay, I had a series of unfortunate things happening, but your answer was the correct one ..
When I edited the line to:
implementation "com.esotericsoftware.spine:spine-libgdx:3.6.53.1"
then it removed 3.5.51.1 and instead put the example files I had put into core, as the library.
.. and it just kept getting worse with stranger things happening, in the end I just deleted the whole project and added libgdx and the correct spine version right away, and what would you know .. it works ..only took me 17 hours to fix 😃
Android Studio is a bit wonky ^^;; Anyway, thanks for putting me on the right track.