This can happen if you manually go to the link in the browser prior to installing Field Maps app. Here are a few workflows that have been used to successfully to clear out Safari as the preferred option to open app links:
1. Uninstall and reinstall Field Maps
2. Go to https://fieldmaps.arcgis.app in Safari, swipe the page down for the Smart Banner to appear, just under the URL banner. Tap the blue OPEN button in the Smart Banner seen in the image below. This should give preference to Field Maps over Safari next time link is opened.
3. Press and hold on the app link from an email, text message, etc. This will present the option on how you’d like to open the link. If you chose the option “Open in Field Maps” it should remember this for the next time.
I hope these help!
Regards,
Colin
Regards,
Colin