[ruraljuror]

I think you could interpret the situation as your employer being dishonest (it sounds like it, and that is troubling) or you could say they have will to do things with tech like React or TS, which could be an opportunity for you.

This could be stating the obvious, but legacy code does not necessarily correlate to age. A really bad situation is where your team is actively writing legacy code: written today, needs to be replaced tomorrow.

I have been involved with a greenfield project which replaced a legacy system which was actively being used. My team's decision was to scrap the old and start from scratch. This resulted in a massive delay before we were able to start adding value for our users. While we spent over a year using (learning) newer tech to build a system from scratch, they were stuck using the old system. And of course the new release was buggy.

A much better approach would have been to incrementally introduce the new tech were possible until it replaces the entire system. I think the pattern is called strangler vine.

Working Effectively with Legacy Code by Michael Feathers is a classic. It might be helpful or get you more interested if you are not already familiar.