I have a project with the links stored in the fields. I follow the documentations, and it is not possible to create a hyperlink.
Project: https://app.merginmaps.com/projects/lutraconsulting/problem_with_Hlink_and_back/tree
Layer: Detaljplaner
Fields: Ext_sokvag

The form in the app appears either as the link, or Open file which is not clickable. Clicking on it results in this: #3525