Could you please share where did you read that? (I would like to know the reasons why is not recommended, given the fact both SSD and USB use NAND flash)
My PureOs10 dev SO is running on an usb 16gb almost 4 months ago. (march 4 2022 )
I haven’t had issues till now. The Lenovo U-430 Touch has one usb 3.0 port.
Noone is saying that it won’t work, only that it is not recommended.
Comparing a portable SSD and a flash drive, in either case via USB, the former will typically give higher performance and give greater reliability after a large amount of writing. You get what you pay for.
Use sudo hdparm -t on your USB flash drive in order to see what its read speed is.