How to update the boot menu after rolling back system generations?

I have rolled back the system generation with
nix-env --profile /nix/var/nix/profiles/system --rollback
But the default entry in the boot menu is still for the most recent generation.

How do I get it updated and reflects the rollback without modifying the grub.cfg manually (I use grub)?

nixos-rebuild --install-bootloader boot is not what I want. The system on my laptop simply cannot be upgraded, or some Qt or plasma stuff will break (issue 97157).

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