Two Macs, two copies of macOS Photos library

I use iCloud Photos, I have a late 2013 iMac that supports only as late as Catalina, and an M1 Mac mini with 250Gb internal storage. I just moved Photos Library on the iMac to a basic Seagate 4Tb external drive - the reason I did this was so I could enable 'Download Originals to this Mac' in Photos preferences and do video editing in iMovie. Unfortunately Catalina does not support the current version of iMovie, so then I need to use it on the Mac mini. The problem with the Mac mini is the small amount of internal storage. My iCloud Photos library is about 283Gb in size. I have a 128Gb thumb drive. Is there any reason I shouldn't use that drive, connected to my Mac mini, to store the other copy of the Photos Library?

The advice given by Apple is that you should 'Make sure that your external storage device, such as a USB drive or Thunderbolt drive, is formatted for Mac: either APFS format or Mac OS Extended (Journaled) format - but not to use removable storage device like an SD card or USB flash drive, or on a device shared over your network or the internet, including over a cloud-based storage service.'

Isn't a USB thumb drive equivalent to a USB flash drive?