There's a MicroSD slot on the Surface Pro 7. It's underneath the kickstand so it's protected. No need to open anything to add a chip. It clicks right in. I added a 512 Gigabyte chip in that slot, and it shows up as a D drive. Not every software application will load to this drive, but some will. And it's great for picture, video, and file storage, of course.
Cost for a 512Gig chip was less than $80.