I negde help with dual booting with latest Fedora

I've tried to dual boot with Fedora, NixOS being installed first, but now GRUB menu shows only options for Fedora and I lost my precious NixOS installation. Already tried everything described on Fedora wiki and various Internet sources, but to no avail. Worth mentioning that both os-prober and grub2-mkconfig finds Nix installation but it is not added to grub config.