SSRS 2016 report is failing with 'EXCELOPENXML' render format error

Few reports are failing with 'ExcelOpenXML' render format error after rs migration from 2014 to 2016. I made following change to the RS config file so I can use old excel format however some of the reports are using 'ExcelopenXML' format. How can I use both 'Excel' and 'ExcelOpenXML' format so report will be sent out based on render format setup in subscription?