This question is related to these. But none of the solutions worked for me.

Yarn can't find private Github npm registry
Installing private package from Github Package registry fails with not found/not authorized

I can install a package without issues with npm install @scope/package however I cannot do the same with yarn: yarn add @scope/package

yarn throws the following error: An unexpected error occurred: "https://npm.pkg.github.com/download/@scope/package/1.2.8/089b08cffb16074c210ec3a59b04de268ae1c7b3a0492dce110adee3ada05bdd: Request failed \"401 Unauthorized\"".

my .npmrc file looks like this: (tried with and without below .yarnrc)

registry=https://registry.npmjs.org/
//npm.pkg.github.com/:_authToken=MY_AUTHTOKEN
@scope:registry=https://npm.pkg.github.com/

I have tried adding this .yarnrc file:

registry "https://registry.npmjs.org"
"@scope:registry" "https://npm.pkg.github.com"

(without .yarnrc) I've tried this .npmrc file

registry=https://registry.yarnpkg.com/

@scope:registry=https://npm.pkg.github.com
//npm.pkg.github.com/:_authToken=MY_AUTHTOKEN
always-auth=true

Where MY_AUTHTOKEN is my Personal Access Token I've generated from Github. (it has access to everything in packages)

I have tried to:

remove yarn.lock
remove .yarnrc
login with npm login using my PAT as the password
logout of npm and removing global .npmrc and .yarnrc
logging in with yarn login

In case of any confusion I'm not actually trying @scope and /package but my actual scope and package name.

I do have access to the scope and package on Github.

and again my first setup works just fine with npm. But I cannot get this working with yarn, and cannot find any valid existing solution on SO.

The following worked for me in .npmrc

@mvce-superstars:registry=https://npm.pkg.github.com

Using yarn v2, the following worked for me in .yarnrc.yml:

npmScopes:
  "mvce-superstars":
    npmAlwaysAuth: true
    npmRegistryServer: "https://npm.pkg.github.com"

Firstly, note the lowercase scope name. This is supposed to be the name of the owner of the repository (MVCE-Superstars) where the package was published, but the name has to be all lower-cased.

The setup

Publishing

I created a private copy of this hello-world repository.
I copied over the above .npmrc OR .yarnrc.yml file into the repoository.
Next I logged in using the npm login --registry=https://npm.pkg.github.com/ OR yarn npm login --scope=mvce-superstars command
I entered my github user name, and my token (with scopes read:package, write:package, and repo)
Finally, I pushed the package to my private repo using npm publish OR yarn npm publish