Hosted Onboarding isn't supported inside a webview - https://docs.stripe.com/connect/custom/hosted-onboarding#supported-browsers

SFSafariViewController is similar to a "web browser" view so it behaves like a safari tab but inside your app. So you can't launch your app from within the app. This other answer explains it

So the only option is to have the app open those links in native Safari on mobile + use the universal link