Did you format that card as 'internal' (a.k.a. adoptable) or as 'portable'?
If the former you typically don't interact with the card as it's now more or less just an extension to your phone's internal storage. It's file structure has been altered to match the same file system that your phone is using (ext4) and it's been encrypted with the encryption key tied specifically to just your phone so removing it and trying to access its contents on a computer just won't work out. (... and normally when set up as 'internal' you should just leave the card as is and not remove it anyway.) Using a file manager app on your phone will only see it as an extension to your phone's internal storage, not as a separate storage media.
If the latter, the card remains its default file system (FAT32 or exFAT) and typically should work as just transfer media to and from a computer. And you should be able to access it directly using a file manager app on your phone to transfer files and such. So in this case then there is a problem, since you can't do any of that. If it was previously formatted as 'internal' than you need to reformat it as 'portable' to use it as typical microSD card again if you want to remove/insert it to transfer files to and from your computer.
But it sounds like the card is currently formatted as 'internal', yes?
