I believe WinUSB library it its probably simplest solution. On the other hand why not to use simple hardware solution like serialusb converter and with build in STM32 usart you can get up to 4,5 Mbaud/sec it itis 450kB/sec is it enough?. I would probably dig in more into STM32 usb (give yourself at least 2 weeks) but if you are in a rush you may consider this.
PS. I use profilic converter (pl-2303) from old mobile phonecable mine goes nuts above 1Mbit/sec but mine friend has it on board and can go easily up to 3Mbit/sec. Watch out for this issue.
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