All distros “support” SB because SB is not part of Linux and it requires setting your own SB keys. That is outside of easy scope. The question is if they support the m$ signed shim and what system is used to achieve this. Fed uses Anaconda (unrelated to Python container system). It is something unique to Fedora as far as I know. Linux refuses to support SB because SB is a scheme to steal hardware ownership. The standard implementation is only a suggestion and bootloaders are not required to give you access to the custom keys implementation in the specification. Microsoft controls the shim for SB. It is extremely decisive and controversial.