I am unable to copy file from my MacBook Air OS 12.6.3 to Extreme SSD (format APFS). That said, the Time Machine seems to be backing up to it just fine.
Have you opened a Support Case? If not opened, for more information, please contact the SD Technical Support team for best assistance and troubleshooting:
On your Mac, select the item, then choose File > Get Info or press Command-I.
Click the arrow next to Sharing & Permissions to expand the section.
Click the pop-up menu next to your username to see the permissions settings.
If you’re not logged in as an administrator, you may need to click the lock to unlock it, then enter an administrator name and password (or use Touch ID or your Apple Watch).
Change the permissions to either Read & Write or “Read only”.
If you need to, also change the permissions for the location where you want to put the item.
Remove unnecessary files to save space.
I had a similar issue with my external hard drive a while back, and it was super annoying. You’ve tried different media players and file managers, but it seems like the problem is with the SSD itself.
To be safe, you could use a backup software like EaseUS Todo Backup to save your important files. It’s user-friendly and has different backup options. Another option is using EaseUS Data Recovery to retrieve lost or corrupted files. It’s powerful and easy to use, with a free trial available.
You might also want to contact SanDisk’s customer support to see if they can help or if your SSD is still under warranty. Good luck!