Hi Mamuka,
It seems error occurred when you created a data source under on-premise data gateway, right? Did you get data use Oracle data source or via ODBC driver?
From the error log, I find error message:
Microsoft.PowerBI.DataMovement.Pipeline.Diagnostics.MashupDataAccessHostingException: A problem hosting the mashup engine was detected. Reason: Timeout. Error code: -2147467259
I would suggest you contact your Oracle admin to increase query timeout value on Oracle side.
Also please check if the machine hosts the on-premise data gateway can access Oracle server. If there is a Oracle client installed in that machine, please test in Oracle client to get data from the same server to see if the issue occurs.
If you have on-premise data gateway( personal mode), please configure the dataset use personal mode gateway then check if you can enter credential for data source successfully.
Best Regards,
Qiuyun Yu