Private NPM registry issues

I had never been able to update my private registry packages with dependabot, so I gave up on it because it wasn't a big deal to me that my private packages were not able to be automatically updated. My main concern were all public dependencies and they worked fine. That is, until yesterday.

Yesterday, it started failing with these errors:

Error whilst updating jest-fail-on-console in /yarn.lock:
Couldn't find package "@mediahuis/chameleon-react" on the "npm" registry.

So, somehow, public dependencies are now a problem as well? (I guess because they are dependencies to my private package?)

I tried again today to add my private registry config to my dependabot configuration. I feel like I tried every possible combination of configuration found in documentation, issues, blog posts, ... (with token:, with username: and password:, with different users, with and without base64 encoding, with different URLS, ...) But alas, I can't seem to get it to work. It keeps coming back with

[2022-05-31 14:26:29 +0000] INFO  -- [dependency-update: frontend/chameleon=>npm]   updating jest-fail-on-console: 2.4.1 => 2.4.2
[2022-05-31 14:26:35 +0000] ERROR -- [dependency-update: frontend/chameleon=>npm] core helpers failure: {"command":"node /opt/npm_and_yarn/run.js","function":"yarn:update","args":["/home/dependabot/app/tmp/dependabot_20220531-10-1elvxop",[{"name":"jest-fail-on-console","version":"2.4.2","requirements":[{"requirement":"^2.0.4","file":"packages/chameleon-react/package.json","groups":["devDependencies"],"source":{"type":"registry","url":"https://registry.yarnpkg.com"}}]}]],"time_taken":1.70834458,"stderr_output":"","process_exit_value":"pid 233 exit 1","process_termsig":null,"response":{"error":"Couldn't find package \"@mediahuis/chameleon-react\" on the \"npm\" registry."}}
[2022-05-31 14:26:42 +0000] ERROR -- [dependency-update: frontend/chameleon=>npm] Error whilst updating jest-fail-on-console in /yarn.lock:
Couldn't find package "@mediahuis/chameleon-react" on the "npm" registry.

Does anyone have a working set up with a private NPM registry? My private registry is on Azure Artifacts (if that matters..).