We had a requirement to do a fresh disk install of OS X Catalina to a MacBook Air that was on Mojave. USB C to USB converter in hand, bootable USB with the Cataina install.app on it.
Macbook Air does not see the USB via the connector when it comes to installing the new OS. Can’t install from something not seen. Installing from the Internet Recovery option offered Mojave reinstall. No.
Turns out you can force the Internet Recovery option by pressing CMD + OPTION + R when the mac boots, instead of just the OPTION key.
To get round installing it – use Disk Utility and wipe drive – go back to MacOs Utilities and choose Reinstall OS. Assuming you’ve connected to a network, it will offer the latest OS, download and install.