Trying to use inst.updates=https://... on a Fedora IoT installer image - at least osbuild-built ones, I tested with an F40 image - does not work, because the initramfs environment has no /etc/pki/tls/certs/ca-bundle.crt file. curl is expecting to find this (it's the system trusted certificate list) and refuses to run without it, so you get an infinite loop of "curl: (77) error setting certificate file: /etc/pki/tls/certs/ca-bundle.crt" errors.

This is not the case with a Silverblue image I tested (Silverblue images aren't built with osbuild) - /etc/pki/tls/certs/ca-bundle.crt is present in the installer environment, there. I'm really not sure exactly how the initramfs environment is constructed in each case, off the top of my head.