As stats on iOS usage, indicating that iOS 9.0-9.2.x usage is currently at 0.17%. If these numbers are truly indicative of global use of these versions, then it’s even more likely to be safe to remove shrink-to-fit from your viewport meta tag.
After 9.2.x. IOS remove this tag check on its' browser.
You can check this page https://www.scottohara.me/blog/2018/12/11/shrink-to-fit.html