I think the 18W charging adapter reduces the battery health of iPhone. I have an iPhone 11 Pro and I tried not to use the 18W adapter but instead, used the iPhone 11 (not Pro) type slow charger to not wear down the battery. So in conclusion, just try to avoid fast charging as much as possible. My battery health stayed at 100 percent for about two months from when I brought it.
Yes; yesterday I read all the 11 Pro details at Apple website and they are also telling that only when you are on hurry then you can use fast charger which they provided with the mobile. Even they are not recommending to use this for all time. M