Hi Ally,
the CF4 does not detect devices or operating systems so it also does not work differently based on your device.
The responsive template only works differently on several screen resolutions.
And I think there is your problem:
On the Desktop you have the flyout-menu on the "bell" where you can also find the "Topics last 24h" Link.
On mobile you only find the link to the active topics the last 24h on the forum index.
If you are logged in those buttons will be replaced with the "Unread posts since your last visit" because that's more important for many logged in users wich topics are acually new since their last visit and not wich topics were there the last 24h.
I'd suggest you add the Link to the last 24h active topics to the mobile menu as well. So if you're on mobile AND you are logged in you can still access the 24h Link via the burger-menu on the top right.
Open header.htm from your template for that
FIND
Code
{if $LOGGED_IN}
<li><a href="search.{$EXT}?mode=upi">{$LANG.tbx_01}{if $G_UPI_TOPIC_COUNT>0} <div class="uk-badge uk-badge-notification uk-badge-danger cf-nav-badge">{$G_UPI_TOPIC_COUNT}</div>{/if}</a></li>
<li><a href="search.{$EXT}?mode=markread&all=true">{$LANG.mark_all_forums_read}</a></li>
{/if}
REPLACE WITH
Code
{if $LOGGED_IN}
<li><a href="search.{$EXT}?mode=upi">{$LANG.tbx_01}{if $G_UPI_TOPIC_COUNT>0} <div class="uk-badge uk-badge-notification uk-badge-danger cf-nav-badge">{$G_UPI_TOPIC_COUNT}</div>{/if}</a></li>
<li><a href="search.{$EXT}?mode=markread&all=true">{$LANG.mark_all_forums_read}</a></li>
<li><a href="search.{$EXT}?mode=24">Active topics the last 24h</a></li>
{/if}
Then you have in the menu the "Unread" - "Mark all Read" and below that the "Active topics the last 24h".
Sincerely,
Chris