I have a dual Fedora/Windows system. I am considering upgrading to Windows 11, and I was thinking if it would be possible to simply back up the necessary files from /boot and restore those after the upgrade is complete, instead of the whole booting from a live distro and reinstalling grub.
Do you current have windows 10 installed?
If so the fedora boot files should not get touched.
You should be able to change the boot order in the UEFI bios to boot into fedora again.
Is your disk partitioned using GPT or legacy MBR?
Windows 11 will want GPT which windows has a tool to do the convert from MBR to GPT.
If you have do this then installing grub will be necessary to add the uefi files.
Ah, that’s great 
I have GPT, so I should be able to fix it in the BIOS, then.
All information I could find is about reinstalling grub. I will report later, hopefully this is of help to someone else.
More important is to have good backups of critical data from Fedora and Windows 10. Upgrades involved a lot of mass storage operations, and can push drives that are close to failure over the edge so you need a way to recover if the update fails.
I have dual boot Windows 10 on one Dell system using an external drive (linux runs well on external USB3 SSD’s) so I can protect linux data from Windows misfeatures. I also have Windows 11 on another Dell system but sharing an internal drive. Windows 11 updates often mess with the UEFI boot order, and leave Windows 11 hybernating, so the system reboots directly into Windows. Windows 11 Recovery Options can be used to get the UEFI settings on my Dell systems and make Fedora (actually the grub2 menu) the default. Other venders may be different.