I have a dual sink. The one side drains perfectly fine but the side with the garbage disposal does not drain or drains very slow. The garbage disposal no longer works and really don't want to replace since I never used it in the first place. I have tried using a plunger on it and a liquid draniner but still does not drain.
Not sure whatelse to try.

Since one side drains and the other does not, you must have a trap for each side. The blockage would be in the trap. Remove the trap on the garbage disposal side and clean.