Qubes OS Installation Error

Version R.4.2.1 ISO installed on a USB drive using Rufus using the GPT partition scheme

Got this error after booting into the USB drive and selecting to install Qubes OS R.4.2.1 (I restarted the setup and got the same error again):

Did you write the ISO on USB in DD mode in Rufus?

Oops I didn’t notice that section of the guide, thanks!

Btw, is it fine to install in GPT partition scheme or does it matter?

It’s fine, you need to use GPT for UEFI.