hi @der 

First of all thank you for your patience and for providing more information about your case.

Use of ".format("excel")"

I replicated equally your cluster config in Azure. Without installing any library, I was able to run and load the xlsx file using ".format("excel")". Unfortunately the documentation does not mention about it, and at this point I'm not using "dev.mauch.spark.excel" library

Then I proceeded to check the "SparkUI" and identified within the "SQL / Dataframe Properties" for "spark.databricks.sql.excel.enabled" with value "true".

You can check this configuration by executing the following code:

spark.conf.get("spark.databricks.sql.excel.enabled")

Next I disabled it to test it:

spark.conf.set("spark.databricks.sql.excel.enabled","false")

With this configuration now I was able to replicate the issue:

With this said, please on your cluster, enable this configuration and try again to read the file

spark.conf.set("spark.databricks.sql.excel.enabled","true")

 Use of ".format("dev.mauch.spark.excel)""

Then I installed the "dev.mauch.spark.excel" and was also able to use it as well.

Conclusion

This behavior highlights that these two implementations are separated and that ".format("excel")" leverages "spark.databricks.sql.excel" instead of the expected "dev.mauch.spark.excel". I agree that is a bit confusing while updating API versions where both use "excel" as format value.

 I hope this helps and if it does, please Accept as Solution.