Hi Danny,
Thank you for posting your question here! I totally understand your frustration here but let me explain it to you.
The new Paint changes pixel colors slightly when you copy paste or rotate which breaks the fill tool This is not user error It happens because the modern version uses new color handling and scaling. The old classic Paint handled pixels exactly as they were. Sadly, uninstalling and reinstalling or looking for a 32-bit version will not bring the old one back Microsoft removed that path.
Let me know if you need further assistance, feel free to ask me by clicking "Add Comment" or "Add Answer" if you cannot add comment so your response will be visible. Thank you and I appreciate your effort.
Regards,
Angelique P.