Hi Medplum team, I feel like this is probably not an intended use-case but we really love the medplum app UI for looking into FHIR resources when developing. Is there a way to use the Medplum UI with for example our own HAPI FHIR server? Like MySQL Workbench for SQL server.

It is not really intended ... you could consider switching to Medplum for the backend! Might also consider Vanya? https://vanyalabs.com/

Yes Vanya looks like exactly what I was looking for - not quite as neat as medplum's ui but will do the job, thanks!