https://www.youtube.com/watch?v=sM0QhtYzdoY

One more time. Dynamic comparison is for adding products dynamically.

Static ids is for listing. Its not for adding products. Its just for
showing SPECIAL products. For example, to show best products which you want
feature on site. Its not for comparison, adding new products will not work
because adding product requires calculation for categories, attributes and
dynamic scripts which you disable once you use special ids.

We will remove this button for shortcode in next update to prevent
confusion. If you need dynamic comparison - use dynamic comparison.

From a visitor perspective when he lands on a particular post review which has static items already prepopulated (including the product which post review is about), I am sure it would be very beneficial to also have the option to add more other items to the comparison. As you can't hope visitor will find and use a dynamic comparison page unless you highlight that option across the whole site.

The right side compare icon only appears when you already add something to compare. Maybe if that button with compare icon on the right side of the site would show all the time (it seems it doesn't show on posts if static items shortcode is used and on other parts of sites only if you already add something to comparison). And if it would have an integrated option to search and add products for comparison and not just to see already added products, it would be perfect.

Maybe add an option to show related products below static comparison which you can add to the comparison.

Giving the opportunity to see the pre-selected comparison and add/remove products would be very beneficial to visitors. People don't like to work much, they want information asap.

Also, it seems the comparison icon is not exactly visible on the products archive unless you hover over the image, and it is really small in other places too. Maybe because I use clean Rehub with no special child theme.

These are just ideas. I think the comparison option would become more useful with additional improvements would be added. Hopefully, you will take some into consideration. For now, I will use as it is.

so, add next parameter searchbtn='' to shortcode to hide button. We will
hide it by default in next update

add to compare is working only on dynamic comparison page

It has no sense. Because when you add ids, page will work as listing and
not as dynamic comparison. it means that page will show static items. This
is purpose of ids parameter

So you are saying that it is not possible to have working  “Add more items” button and add product ids?

Is it possible to somehow make it work?

When you add ids, this page is working as listing and not dynamic
comparison. So, you must add also parameter to disable button

When I use shortcode [wpsm_woocharts disable="description,brand,stock,userrate"] on comparison page “Add more items” button works.

But when I add shortcode [wpsm_woocharts ids="480,291,326,377" disable="description,brand,stock,userrate"] to display pre-set comparison products on posts with option to add more items, the  “Add more items” button doesn't work. It shows, but when clicked nothing happens.