I need a minecraft nbt creator online?

Unfortunately I don't find any myself

you should be able to edit command block in minecraft

http://mcstacker.net

Then you go to "data merge entity", enter "chest minecart" and then you get along yourself.

You can't use NBT in commands in the Bedrock Edition. Therefore there's no NBT Creator.

you can use it in bedrock with horion client by copying the created nbt then writing .nbt load in the chat