Question on tracking

Until ADS-B is required, can a private pilot “turn off” the transponder to keep a flight path private?

Yes and no. If the aircraft is in airspace that requires a transponder then it must remain on. This won’t change.

If outside of that airspace then it could be turned off.
It messes with TCAS and SAR so doing so would be at your own risk. The aircraft can still be tracked by radar. The altitude is hard to work out without a transponder.

There are exceptions for aircraft without electrical systems. Generally they make prior arrangements for the safety of everyone.

If a flight was being tracked by radar (assuming the transponder was turned off)–would it show up as an active flight on Flight Aware? Thanks for answering–I am new to this.

No. There is no way to uniquely identify it.
They could work it out reviewing the data and have a guess.

Search faa.gov and google for how radar works.

We don’t receive uncorrelated primary radar in any of our coverage regions.

We may be able to provide tracking to the operator if they’re a customer and sending us their datalink (ACARS, etc).

Thank you so much for your responses!