the first page is not filled entirely, but it already created other pages after excluding/hidding particular taged products.

{% for product in collection.products %}
  {% if product.tags contains 'hideProd' %}{% continue %}{% endif %}
  <!-- your product grid item -->
{% endfor %}

Gaps should fill.

For example, if there are 100 products in a collection and the pagination is set to 5 pages (with 20 products per page), but 20 products are excluded or hidden, the pagination should adjust to display only 4 pages.