Sorry if being silly but how do we take baby food on long flights? I check that they dont have microwave so they cant reheat food in that but they do reheat food in hot water. As my girl is 20 months now, I want to give her proper food

You could prep something and bring in a insulated food container.
Or check the flight menu to see if anything suitable.
We've only done short flights so far and eaten in airport, and had fruit, cheese, crackers etc for actual flight.

Just eat our meals on the flight + snacks.
Even though they don’t get their own food (if you travel with them on the lap), often flight attendants wouldn’t mind giving extra meal out if flight is not busy. We got entire pack of milk (1l) on our flight to New York, just because I asked for milk for my toddler and they didn’t have anything smaller:)
Or order from hot meals menu on board.

Honestly for 20 months old they might not be so keen to reheat your own food.
I think most of food exceptions and special treatment is only applied to baby milk/formula.