USB flash drive detected but not mounting

[null]

Pi Model or other hardware: 3 Model B Rev 1.2
Power Supply used: CanaKit Model DCAR-052A5 5V 2.5A
RetroPie Version Used (eg 3.6, 3.8.1, 4.1 - do not write latest): 4.8
Built From: raspberry pi imager
USB Devices connected: lsusb output:

Bus 001 Device 006: ID 1cf4f:0002 SiGma Micro Keyboard TRACER Gamma Ivory
Bus 001 Device 005: ID 0079:0011 DragonRise Inc. Gamepad
Bus 001 Device 004: ID 05dc:a701 Lexar Media, Inc. JumpDrive FireFly (this is my USB stick)
Bus 001 Device 003: ID 0424:ec00 Standard Microsystems Corp. SMSC9512/9514 Fast Ethernet Adapter
Bus 001 Device 002 ID 0424:9514 Standard Microsystems Corp. SMC9514 Hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

Controller used: Vilros retro gaming USB NES controller
Error messages received: end of dmesg -w output:

usb-storage 1-1.2:1.0: USB Mass storage device detected
scsi host0: usb-storage 1-1.2:1.0
scsi 0:0:0:0 Direct-Access LEXAR JD FIREFLY 1100 PQ: 0 ANSI: 0 CCS
sd 0:0:0:0 Attached scsi generic sg0 type 0
sd 0:0:0:0 [sda] 987136 512-byte logical blocks: (505 MB/482 MiB)
sd 0:0:0:0 [sda] Write Protect is off
sd 0:0:0:0 [sda] Mode Sense: 43 00 00 00
sd 0:0:0:0 [sda] No Caching mode page found
sd 0:0:0:0 [sda] Assuming drive cache: write through
sd 0:0:0:0 [sda] Attached SCSI removable disk

$ ls -a /media/usb
. .. usb usb0 usb1 usb2 usb3 usb4 usb5 usb6 usb7

All the above directories are empty.

Guide used: https://retropie.org.uk/docs/Transferring-Roms/
Emulator: nes
How to replicate the problem: format usb flash drive to fat32 or exFAT, create retropie directory, plug into retropie and wait for activity light to stop, directory structure is not copied. Manually add /retropie/roms/nes/ directory to flash drive and add .nes roms, plug into retropie, wait for activity light to turn off, files have not been transferred.

I'm having a similar issue to USB Drives Not Connecting, which wasn't resolved. I've tried two different USB flash drives, one formatted to fat32 and the other exFAT. They appear to be detected when plugged in, but they're not mounting properly, and thus roms aren't being transferred. I've confirmed that the usbromservice is installed and running.

In the other threads about trouble with USB drives people have suggested just transferring the roms some other way. I'm setting up this retropie as an NES emulator for my 4-year-old, and I only intend to give him a few games at a time to keep them special. I was actually already planning on writing a small script to transfer games automatically to the pi from a USB stick so I could 3d print a case for the USB stick that looks like an NES cartridge and give him new games for birthdays/Christmas. So being able to transfer games via USB is a significant part of the experience I'm going for. Plus it seems like something that really should work, so it's frustrating that it doesn't and I'd like to fix it if possible.

Thanks in advance for any help!

[mitu]

Your flash drive has no partitions defined. Add 1 primary partition and format it, then repeat the set-up process again (create retropie folder, insert into RetroPie, etc.).
BTW, if your Pi is connected to your network, you can transfer the ROMs via file shares or SSH, without an USB drive.

[null]

@mitu This worked! I was surprised, because after formatting the flash drive it looked like the drive had a single partition taking up the whole volume. I wasn't able to create partitions on Windows 10, so I used the Disk Utility on macOS to create two exFAT partitions (screenshots of the volume in Disk Management before and after below). After that I was able to follow the instructions to create the proper directories and transfer the ROMs!

Thanks!