You’re not wrong here but usually this comes down to having one or a small number of version specific container processors (and I do not mean container in the docker sense) to host those functions. Not microservices.

That said, almost always, if you are seriously trying to keep old unsupported dependencies running, you’re violating any reasonable security stance.

I’m not saying it never happens, but often the issues that the code is not understood, and no one is capable of supporting it, and so you are deep in the shit already.