Huh, so loading a picture directly from a USB drive works and PixelCNC doesn't crash when opening a project from there either. I messed with security and access stuff some more but didn't find any solutions there. I also didn't have that unblock option in PixelCNC.
I'll see if any issues arise from having the files on a USB stick. I'll be getting a proper new PC in the near future, so not a huge issue if this solution doesn't work properly.
Thank you for the quick response!