I just installed Silverblue, but somehow this removed Windows from the EFI entries. After some searching on the internet I managed to fix that, but it seems I accidentally removed the fedora entry now. How do I restore Silverblue’s EFI entry?
You have to use a live usb to do so.
sudo grub2-mkconfig -o /boot/grub2/grub.cfg
Only do so when properly configured and in the chroot environment for the actual installed system. If the installed devices are not properly mounted and you are not in the chroot environment then this would not work.
Reinstall with not checking your home partition for formatting (in advanced disk layout). This will restore your fedora installation and is easier than trying to modify grub menu in Silverlbue. Since you have just installed Silverblue, there should be minimal/no loss of data in your case.
If you are using just one disk in your system, then you would make sure the proper mount points are set in the advanced disk layout menu, subvolume layout. For the typical install this is
/home mount points as listed in the subvolume layout (below the partition layout) in the advanced disk layout menu. As well there is a ESP and EXT4 partition (in normal setup) the ESP was overwritten by WIndows (likely) when you fixed it’s missing boot entry. Make sure it’s about 1GB. The EXT4 partition will hold the actual initrd file for your system, this is the second stage of the boot process (for simplicity sake). You do not want to format the ESP unless you want to re-install windows. General rule of thumb is windows install first, fedora second. If windows needs to subsequently repair itself, you will likely have to repair your Silverblue grub menu again. The live USB does have some troubleshooting options available which will let you boot the Silverblue installation, and may be a good route to choose for repairing without re-installing.