I encountered the same problem.
I turned off BitLocker on both the 980 Pro 2TB drive and the system drive, which is a Samsung 512GB NVMe. On Windows 11: Control Panel > System and Security > BitLocker Drive Encryption.
Magician then performed the firmware update as expected.
You might be able to simply pause BitLocker.
Samsung Magician should be able to do this automatically, or at least notify you to pause BitLocker.
Of course, it is a good idea to backup your data before performing a firmware update.
I build 6 PC a year ago. Asus x570 dark hero, ryzen 5950x. And 980 pro 2TB. Now after 1 year 5 0ut of 6 drives are broken. Magician is completely useless. Repair fails always. I now exchanged all with firecuda530. Cloning took hours of chkdsk repairs and finding the right program tolerating the totally faulty 980Pros. DO NOT USE 980PRO! JUST GOOGLE IT. SAMSUNG KNOWS FOR LONG TIME THAT THOSE DRIVES ARE NO GOOD AND IS NOT DOIBG ANYTHING!
Most probably your drive is already half in the dumpster and that's the reason the firmware update doesn't work. Do NOT look at Magician....even it says drive is gòd, run the long test and be prepared that this reveals lots of unreadable sectors. This drive is certified garbage. And I am a samsung fan boy...