Hi Olliver
I am Dave, an Independent Advisor, I will help you with this . . .
Typically Blender is not installed into the Program Files Folder, it is a Standalone Application that can run from any folder, and due to the amount of Plugins . . etc. required for Blender, it is best to not install Blender into the Program Files folder
On that Security Tab, click the Add Button and add a new User, name it: Everyone
Then give that user full control on the Blender folder
Then check if you can access that folder . . .
.