I feel this is not an immediate fit with your report … but … there is a recent unresolved thread where I went through some troubleshooting steps based on the idea that a corruption might have occurred due to a known SD card installation issue explained thoroughly here https://forum.fairphone.com/t/a-little-guide-to-using-sd-cards/37297. Conceivably (unlikely) even if you think you never used your card as “
Formatted as internal storage” some software fault has occurred.
But simplest things first I would be inclined to try to test whether your SD card is (for unknown reason) reaching end of life. This does happen and would is simple to rule out.
In your place I would take out the SD card and check if it is readable on a PC. And re-confirm that the phone is ok without the card.
I would take the precaution to back the card up to the PC, in case the card should deteriorate.
I would buy or borrow a new or newly formatted SD card to check how the phone behaves with a known “clean” card.