I have a lack of knowledge since I cannot figure this out myself. The problem is a new USB flash drive. I thought it would be handy to have a flash drive with both type A and type C connector.
Flash drive: SanDisk Ultra Dual Drive ( Amazon.com: SanDisk 64GB Ultra Dual Drive USB Type-C - USB-C, USB 3.1 - SDDDC2-064G-G46, Grey/Silver (Pack of 3) : Electronics ).
KDE recognize it as USB 3.1 Gen 1 flash drive. NixOS does not mount it; it does not appear in the file manager. Removing the drive, KDE does acknowledge the removal.
All the older flash drives mount as normal and appear correctly on the command line and file manager. Can someone point me to any relevant documentation on this topic? The SanDisk flash drive works normally on my Windows system.
<<<<<<<<<<<<<<<<< Update >>>>>>>>>>>>
I figured out the issue. Looking at the flash drive with Windows, I realized it was formatted as a Windows recovery drive. Hence the format was unusual and not recognizable by NixOS. To those who read my post - Thank you!