Hi Tor,
It relates to the grid column in Bootstrap used for the mainnav block.
I just cloned this block to have a new one called mainnav2
and changed the classes: col-xxl-4 + col-xxl-4 + col-xxl-4 to col-xxl-2 + col-xxl-8 + col-xxl-2as following:
<!-- HEADER BLOCK -->
<header class="header-block header-default w-100">
<div class="header-wrap row d-flex align-items-center collapse-static t4-nav-height">
<div class="col-6 col-lg-2 col-xxl-2">
<jdoc:include type="element" name="logo" data-home="index.php" />
</div>
<div class="t4-navbar col-1 col-lg-6 col-xxl-8 d-flex justify-content-xxl-center collapse-static">
<jdoc:include type="element" name="megamenu" />
</div>
<div class="t4-header-r col-5 col-lg-4 col-xxl-2 d-flex align-items-center justify-content-end">
<span class="d-none d-md-flex align-items-center header-first">
<jdoc:include type="modules" name="header-r" style="raw" />
</span>
<jdoc:include type="modules" name="header-cart" style="raw" />
<span class="d-none d-xl-flex align-items-center">
<jdoc:include type="modules" name="header-cta" style="raw" />
</span>
<jdoc:include type="element" name="megamenu-toggle" />
<jdoc:include type="element" name="offcanvas-toggle" />
</div>
</div>
</header>
<!-- // HEADER BLOCK -->
When you clone a block to have a new one like this, it will be safe on updating new version of template
