A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
Hi Ori,
Sorry for the inconvenience. My understanding is that if Office suite and Excel 2016 themselves work well (open, edit, save), the issue seems to be related to that third-party program or system level. When you want to export file from that third-party app, system cannot launch Excel 2016 in the Office suite.
You could first perform an online repair for Office 365 suite. Check if there are some improvements. If it doesn't work, I suggest post a new thread in our Windows category (according to your operating system version) for getting system level professional support. Meanwhile, you may also check the support forum or channel of that third-party program. See if there are similar threads and suggestions for using the program with Office 365 suite.
Thanks for your understanding.
Tim