Feels like beauracracy but a DACI or RFC etc. can help if the culture supports this sort of decision making.

You list the options, e.g. A combine codebases, B leave as is. Get comments and look at it logically and come to agreed decision.

You have the reason and tradeoffs documented.

The discussion may prompt other wider discussions etc. More senior people may spot patterns. E.g. lets not pay down tech debt X because Y is coming.

Culturally though if no one cares and most people are happy to manually work through the bugs and hate even discussing it then it may be a bad fit for a developer who cant stand working like that.