I have the identical problem in Databricks Apps.  I have tried...

• Reading from DBFS path using mount version `/dbfs/myfolder/myfile` and protocol `dbfs:/myfolder/myfile`
• Reading from Unity Volumes `/Volumes/mycatalog/mydatabase/myfolder/myfile`
  • Also made sure that the App principal had rights to read from the specific Unity Volume
• Reading from S3 path `s3://mybucket/mypath/myfile`

None of these methods worked for me and cannot use Apps until I have a solution for this.