The ending of Mark was not added later. You are listening to heathens who aim to disprove the Bible. I actually wore out my first Bible and had pages falling out of it. Mark was most likely the end of a scroll and its like the cover at the back fell off.
James Snapp on Defending Mark 16:9–20
https://www.youtube.com/watch?v=Nrte4885ldg
A Case for the Longer Ending of Mark
https://textandcanon.org/a-case-for-the-longer-ending-of-mark/
Authentic: The Case for Mark 16:9-20: 2016 Edition
https://www.amazon.com/Authentic-Case-Mark-9-20-2016-ebook/dp/B01EU1OR9O
Authentic: The Case for Mark 16:9-20 by guest contributor James Snapp, Jr.
Last Two Videos on NT Textual Criticism and Askeland on GJW
https://www.curtisvillecc.com/AuthSupplx.html
The Authenticity of Mark 16:9-10
https://truediscipleship.com/the-authenticity-of-mark-169-10/
James Snapp on Defending Mark 16:9–20
https://www.youtube.com/watch?v=Nrte4885ldg
A Case for the Longer Ending of Mark
https://textandcanon.org/a-case-for-the-longer-ending-of-mark/
Authentic: The Case for Mark 16:9-20: 2016 Edition
https://www.amazon.com/Authentic-Case-Mark-9-20-2016-ebook/dp/B01EU1OR9O
Authentic: The Case for Mark 16:9-20 by guest contributor James Snapp, Jr.
Last Two Videos on NT Textual Criticism and Askeland on GJW
https://www.curtisvillecc.com/AuthSupplx.html
The Authenticity of Mark 16:9-10
https://truediscipleship.com/the-authenticity-of-mark-169-10/