Few Photo taken got grayed out or black out on Note 10 plus. Photos are storing in internal memory and it was the issue way with my S10 plus when I was saving the photos in external storage.
Maybe your micro SD isn't formatted correctly (or possibly too large - likely not - largest is either 256 or 512 GB)...just a suggested try. Reminder: Anything already stored on the SD will be erased if reformatted, so save it somewhere else first...as I recall, saved can be internal OR the SD, but not both simultaneously.
I am saving all my photos in internal memory because I already had this issue with my S10 plus. Nit saving anything in SD card from last 1 and half year. This is something recent