Install 20.04 on external SSD without disabling Intel RST

I tried a daily build of 20.04 in March and was able to install it to an external SSD no problem.

I tried to install a daily build today and the installer is telling me to disable Intel RST before installing.

I don’t want to touch the internal disk, I just want to install to the external SSD but I can’t see any way to achieve that now. Am I missing something?