משתמשים אינם יכולים להוסיף דפי נושאים למסך הנייד (כאשר פותחים נושא)

I don’t think that is possible unfortunately.

The “Add to Home Screen” functionality requires every web app to define a start_url, in which we have defined it as the root URL of your forum.

Here’s what our a2hs manifest looks like: