Can you be more specific on how iOS blocks other browsers? You mean for embedded browser engine in apps?
iOS does not allow third party browser engines. Every browser you download from the iOS App Store is using 'Safari Lite' under the hood. It's ostensibly for security, but it's more about control.
"Apps that browse the web must use the appropriate WebKit framework and WebKit JavaScript." https://open-web-advocacy.org/blog/tim-berners-lee-on-apples...