Found a workaround, not a smooth flow but at least the user doesn’t have to sign in again.
Deploy MS Edge and have the user add their corporate credentials. Once the user opens Salesforce and the webview in safari opens, tap the share button, select open in edge, the user is now signed in using SAML, a pop up shows up asking the user to open in the Salesforce app, select ok. The user is now signed in without having to enter creds.
As I said, not smooth. I would like the see either an extension in safari or a flow that resembles that of other vendors to make it easy for the user.