Saurabh UberEats does not do it that way. The other 2 are Indian companies, so it seems to me it's an Indian thing - maybe Indians don't customize their food as much or aren't as picky. Check out any other big players from different countries and you'll see that the one comment box isn't the common way. In fact, I don't know of any that do it this way outside of India.
But let's talk about it. In what way is the current way best for UX? Say a customer orders 10 different items (is that common in India?) and they want 7 of those items with no salad, or salt, or whatever. The customer would have to enter the names of each item that they wanted to customize separately followed by "no salt" etc. into the checkout box. Then the restaurant would have to read back and forth as they entered the order into their POS system to match the changes the customer requested. What if the restaurant is super busy? What if the order in which the customer entered the comments also doesn't match the order of the items ordered?
What if the customer wants to leave comments for the DELIVERY side of things (which is where the checkout box is usually used), such as ""leave on doorstep"", ""gate pin is ####""? Having them being entered in the same single box as item customizations makes no sense and will just clutter things - the restaurant doesn't need to know about them.
Compare this to having the customer enter the comment as they are adding items to the cart, instead of all at the end. The comment will also appear under the item for the restaurant to easily see so it's not a giant wall of text as it currently would be.
I could understand if your reasoning for not implementing it was because you're busy and have other things to do, and I understand Foodomaa is based off Indian ordering and there are obvious cultural differences.
But to say that having one comment box for everything is good UX baffles me and I would love to hear your explanation of why you think this and what would be so bad with having comments under each item?
And just to reiterate, I'm not asking you to implement it, just to display it, as the work as already been done on my end.