On my Galaxy S6 Lite, after last upgrade of May, only me can use the SD card. Other tablet's users can't see the SD card: "You can't use SD card because it was inserted while a different user profile was in use".
If I unmount the SD card and remount it with an other user, just him is able to see the SD card.
How to fix it?
In the past, from KitKat onwards guest accounts could not access the SD card. It later seemed to allow access to the root directory on the SD card only but now, this is the latest, which should explain Storage updates in Android 11 | Android Developers
We just got two new S7 tablets and 1TB SD cards to share among users, expecting to load many GB of maps and aerial imagery on the SD cards. Sharing a single user account is not an option. I get this notification when using an additional (not a guest) account. The "Storage updates in Android 11" article linked by Pugs1957 does not explain this. It explains changes to the folders that apps can access on the SD card, but there is no reference to locking out users from the SD card. Based on Google searches resulting in almost no hits, except for 2 threads in Samsung forums (the current thread and this thread, I think this is Samsung-specific.