The thing is I use service connection and I have double-checked, it’s still working.
When I run the pipeline specifically and manually on the branch, it still runs perfectly fine. The tasks and configs are the same.
I go to https://sonarcloud.io/organizations/{my_company}/edit and see that my Personal Access Token (under the section Azure DevOps connectivity management) is outdated.
Update it with a new one and now the PR-automated pipelines start working again.
This is somewhat strange from my point of view because CI-triggered pipelines (triggered from new commits to branches like ‘main’ or ‘master’) are still working fine, only PR-automated pipelines fail.