Hi @miltos,
If you publish your module to the "head-ads" postion, you should edit the class of the div tag block to be able to show on mobile.
Change from:
<div class="d-none d-lg-block">
<jdoc:include type="modules" name="head-ads" />
</div>
to
<div class="d-block">
<jdoc:include type="modules" name="head-ads" />
</div>