Thanks a lot for helping. I’ve chosen the CODING-way (more flexible) and got rid of using DATASETs . And also I was able to solve issue with delaying. The problem was that data took certain time to insert and repeater used to update before loading data in collection. As result, I use function .then() where I update the repeater:
await wixData . insert ( db , itemToInsert ). then (( results ) => {
//here I update the repeater
});