I have a 2/4 bar and I’m changing it into a 3/4 bar, the meter appears different but the bar stays in 2/4, with he metronome clicking two beats and the bar showing 2 crochet rests.
That is standard. When one adds a meter change before an established meter, Dorico expects the altered time to be added/subtracted manually SHIFT + B1q (or -1q) to add (or subtract) a quarter note value, since Dorico cannot guess where in the new measure the altered time should exist.
This will operate differently if Insert has been activated.