Is it possible to perform donation with In-App purchase for amount the user want to donate?
No, in-app purchases can only have predefined prices set in iTunes Connect. You can charge the same in-app purchase multiple times, meaning you can calculate the donation to the nearest Tier 1 multiple and repeatedly charge it, but you can’t have custom tiers. Using Apple Pay to get around this is prohibited by App Store guidelines.
Here’s how PCalc shows the various donation levels:
