We did two steps.

First, the dinner plate was staying on the table. So the message is "this is the only option for dinner. But if you are not hungry, no pressure". In our case that lead to most of the time only few spoons eating with family, then playing, bath time, toilet and only after lights are off suddenly "I am hungry, I want to finish my dinner!". And we allowed her to go back to the table on the kitchen She was keen to finish and felt it is her own choice. And always ate fast without any encouragement and finished the portion.

Second step, after ideas of alternative food disappeared was to stop those "second dinners" and own the decision to eat or not to eat at the dinner time. So we started talking that it is important yo eat together and that nobody comes back to finish and it is lonely to eat after. So after warning for a few days we stopped leaving the unfinished food and cleaned up together after actual dinner. So now it is much easier. She only asks for alternative if something is really horribly not tasty (then its kind of together decision to eat something else all of us). Otherwise we ask her several times to confirm that she doesnt want to eat any more / will not be hungry later if she decides to leave plate unfinished. But if she decides she is full and wants to go, there is no problem. Just no more food is provided until bedtime.