I am facing the same issue sometimes that when change price from product detail page webhook does not call but when change price in variant detail page it calls webhook.
I am using 2021-04 currently. Do we have to update webhook version to 2021-07 to not facing this issue again or this is fixed in 2021-04?
Yes that's correct, this would be fixed for all stable versions. Changing price on that page would fire products/update webhook in 2021-04, we'd recommend bumping up to the latest version if possible. Hope that helps!