USB Flash Drive Read-only But Has Spotlight Folder

You can right-click the USB drive and select "Get Info" to see your permission to the drive. If it shows "read-only" under the permissions section, click the lock to unlock it with your admin account and then change the permission to the USB to "read & write".

If you can't change your permission to the USB in Get Info, check if it is caused by your USB hub. You can disconnect the USB hub from your Mac and directly connect the USB drive to your Mac to see if this issue results from the faulty USB hub.

Still no luck? I think that your USB drive probably has some errors. You can move all files from the drive to your Mac and then reformat the drive. If you even can't access the USB drive now, you can use iBoysoft Data Recovery for Mac to rescue the files from the corrupted disk first and then reformat it in Disk Utility.