Using NUR with flakes is silly, NUR was intended for people who don’t use flakes.
Just use the direct upstream flake itself! In this case - GitHub - Mic92/nur-packages: My personal NUR repository
And the full list of repos is at NUR/repos.json at d39c7ced498d546513270b314d682ac5d7de734d · nix-community/NUR · GitHub