Just installing Fedora Silverblue and realised that if you boot into the USB disk in legacy mode, it does a legacy install. If you boot into it in UEFI, it does a UEFI install.
Wish this was made clear in the interface and you could actually choose what you wanted. I mean, I really think UEFI should be the default no matter what these days with the option to change it if you really want to, no?