I was able to add the registry from the github page using ]registry add https://github.com/JuliaRegistries/General,
relevant thread: Updating registry (recent issue)
but when I followed the instructions displayed after running ]registry up I got the same issue as you
(@v1.12) pkg> registry add https://github.com/JuliaRegistries/General
Cloning registry from "https://github.com/JuliaRegistries/General"
Added registry `General` to `C:\Users\johnb\.julia\registries\General`
(@v1.12) pkg> registry st
Registry Status
[23338594] General (https://github.com/JuliaRegistries/General.git)
(@v1.12) pkg> registry up
Updating registry at `C:\Users\johnb\.julia\registries\General`
┌ Info: The General registry is installed via git. Consider reinstalling it via
│ the newer faster direct from tarball format by running:
│ pkg> registry rm General; registry add General
└
Updating git-repo `https://github.com/JuliaRegistries/General`
(@v1.12) pkg> registry rm General; registry add General
Removing registry `General` from C:\Users\johnb\.julia\registries\General
ERROR: could not download https://pkg.julialang.org/registry/23338594-aafe-5451-b93e-139f81909106/fcd178d2ac9db7a1f07d36abf034c8c7716f40b8
Exception: RequestError: HTTP/1.1 404 Not Found while requesting https://pkg.julialang.org/registry/23338594-aafe-5451-b93e-139f81909106/fcd178d2ac9db7a1f07d36abf034c8c7716f40b8