Advisor going over and unhelpfully modifying my presentation structure and slides
There are simple technical solutions that allow you to avoid unpleasant discussions if you want. Prepare your presentations in LaTeX or export them to pdf format, but do not give your supervisor the source code or editable ppt version. Or simply print the handout for your supervisor and present the talk orally. Collect feedback in a form of comments written over the text. Then go through suggestions and decide, which to take on board and implement, and which not.