Hi, currently (F32) Silverblue doesn’t handle too well existing EFI partition with something inside (using auto partitioning by installer), which is something in your case I assume.
If it is, you can either create a new EFI partition for Fedora SB or reformat existing one (custom partitioning during installation).
It will erase your current settings of course.
In my case, I created new EFI partition and installer found windows boot in other, existing EFI so dual-boot works correctly (although having 2 EFI partitions is kind of a waste, but it works).
More information in bug details: