Is there a solution to this after this long time?
A solution to what? Major releases quite commonly introduce breaking changes in the API - otherwise certain things could never change! It will be the same once Godot 4.0 is released as well. If you're not willing to invest the time to adapt your project to a new version, stick with the old one. Automatically converting code to be compliant with a new release is a very complex task and hardly worth the work: over time it becomes a completely unused feature as everyone already migrated to the new version.