Same problem here. Really grumpy about this!
First, I had random reboots due to a Kodak 256 GB SD Card (formatted as external storage). After the latest update (that would address the random reboot issue), I was notified the Kodak SD Card was not supported. So, I stored the data on the card elsewhere and took the SD card out.
I used the FP3 for a while without SD Card, but the phone appeared to be slowing down. So, I looked whether I could find a list of supported SD Cards for FP3: it does not exist. But I read that the capacity limit was 400 GB. I decided to buy a Sandisk Extreme Pro 256 GB. (I just found out that it is fully compatible with FP2, but that doesn’t mean a thing.)
I put the SD Card in the phone and started it and got the question whether to format it as external, or as internal storage. Since the permanent notification about the external storage annoyed me before, I decided to use it as internal storage. No notifications or error messages appeared, so I thought it would all be alright. Until I received an image in Whatsapp, late in the evening. It failed to download. I wanted to ask what kind of file was sent to me, so I tried to send a screenshot. I selected the edited screenshot and tried to send it, but it wasn’t sent, because ‘the file was not on the SD card’.
I cannot yet determine how much data I have lost.
What angers me, is that this apparently is a known bug. Yet the question after inserting a new SD Card is not “would you like to destroy your data, yes or no”. Instead the question and the ‘yes’ are hidden under one of the options.
This comment from 20 September should be shown on the telephone, instead of in this thread which you are only going to read when it’s too late already:
Don’t format you sd card as internal storage except if you are sure of the implications!
Formatting the sd card as phone storage is known for breaking things on the phone, and you’re not the first one to report problems that occurred when doing this under android 10.
With my limited knowledge of computer systems, it appears that there are two ways (or more) to address the (merged) internal memory: one, used by file managers and the photos app, which successfully reads the storage contents, and one, used by the GMail and Whatsapp apps which does not.
The ‘SD Card Manager’ app, I use, crashes when I ask for an app list, which may be totally unrelated. My FP3, however, did propose to me to move a number of apps to the SD card, right after formatting the SD card,
I would very strongly suggest to only enable the formatting of the SD card as internal storage in the developer mode of the telephone, making sure you only do this when the phone is brand new, or when you are willing to risk losing all your data, or when you are trying to examine and solve this issue.
And also the camera app won’t start anymore (‘camera error’… well, more like storage error)