After fifteen years of writing production software, the engagements where I add the most value tend to fall in three buckets:

Scala / functional codebases — refactoring, migrations between effect systems (Cats Effect, ZIO), upgrading legacy Lift/Play apps, helping a team adopt FP idioms without burning everyone out.
Platform & infrastructure — Kubernetes, Terraform, ArgoCD, GitOps pipelines. Designing the boring parts so they stop being a source of incidents.
Cloud migrations & consolidation — moves between Heroku, GCP, AWS; getting a team off bespoke infra and onto something an on-call rotation can sleep through.