flash vs ssd is night and day difference for write speeds. if you write that frequently to your ventoy and write speed matters to you, you want ssd.
either make it (assemble) yourself or buy one. i have a number of clients using samsung t7 external usb ssd. they seem pretty fast to me.
i don't use ventoy or ventoy-like devices that often, i just use flash.. even some usb 2.0 ones. yea, they take longer to boot up and longer (much longer) to write to, but i don't add or replace iso on them very often.