LSC Mobile App Displays HTML Tag for HYPERLINK Formula Field

This behavior is working as designed. The Salesforce mobile app does not support rendering HTML generated by formula fields as native clickable hyperlinks. As a result, formula fields that use the HYPERLINK function display the underlying HTML markup (for example, the <a href> tag) instead of a clickable link in the mobile app.

Workaround :-

Instead of using a formula field with the HYPERLINK() function, use a standard URL field to store the destination URL. Populate the URL field using an appropriate automation mechanism, such as Flow, Apex, or another supported process. Standard URL fields are rendered as clickable links in both the Salesforce web application and mobile app.