After multiple recent support issues with SanDisk brand USBs, we don't recommend buying SanDisk USBs for Unraid at this point.
Either due to counterfeit devices being sold or a manufacturing change directly from SanDisk, multiple users have attempted to boot SanDisk USBs and found out that they do not register a unique GUID and therefore, cannot be properly licensed with Unraid.
Multiple attempts at contacting SanDisk on this issue have gone nowhere.
For a great rundown on the best USBs for Unraid, @SpaceInvaderOne made an exhaustively researched video on the topic:
(Spoiler) Some of the best flash drives were:
Samsung bar plus
USA ---- https://amzn.to/32TtQyp
UK ---- https://amzn.to/3004ooU
DE --- https://www.amazon.de/Samsung-MUF-32BE4-EU-Flash-Speicherstick/dp/B07CVVHCTG/
Samsung Fit Plus
USA --- https://amzn.to/3hFboha
UK --- https://amzn.to/39vSsOR
DE --- https://www.amazon.de/Samsung-Flash-Drive-MUF-32AB-APC/dp/B07HPWKS3C
BONUS Ones confirmed to work
@ich777 recommendation for Amazon.de users:
https://www.amazon.de/Transcend-JetFlash-Extreme-Speed-32GB-USB-Stick/dp/B002WE6CN6
Kanguru - tested and recommended by @AlastorX50
https://www.kanguru.com/products/kanguru-flashblu30-usb3-flash-drive
https://www.kanguru.com/products/kanguru-ss3
https://www.kanguru.com/products/kanguru-flashtrust-secure-firmware-usb-3-0-flash-drive