After performing all standard troubleshooting techniques we found a solution. 

With office 2013 installed and quick books 2019 , we then installed office 365 on top of this.

after this 365 install quick books recognized excel 2013 and defaulted to export with this.

we then had to repair 2013 to get .xlsx file to default to 2013 as well.

No idea what caused this , I was told the install of 365 could be forcing a different version of .net framework to be used.

Hope this helps someone else , good luck.