It would typically be a web.config in the IIS dir. Honestly, I wouldnt worry about it. Those are rarely changed and if this CU13 2019 and above, those settings are saved:
How to identify custom settings before a CU upgrade?
Arthur Wilson
0
Reputation points
I am preparing to update the latest CU. The instructions warn of backing up customized config files. Since I didn't set our server up originally, I really don't know how much customization has been done or where to look. Is this something you can help with?