Can I hide a H2 of a widget with CSS?

Before you start reading here, please read my comments under the OP’s question.

After some thought and as a last resort, it could be done with some sort of workaround. It’s just an idea and maybe it will get to the point, especially when it comes to mobile views, where it doesn’t make sense anymore. You’ll just have to experiment around there.

So what’s it all about? The idea is to put the <iframe> in a container, set to position: absolute; and pull it up a bit with a negative value for margin-top. Finally, we also need the clip-path property to mask it. NOTE: This is what you need to do for each <iframe>, e.g. Top sights in Bologna, Best Food Tours, etc.

For a better understanding here is a very brief example. The gray area is virtually the container. Of course, it can have the same height as the <iframe> and is only larger for demonstration purposes. The red area, on the other hand, is supposed to represent the <iframe>. Finally, the Lorem Ipsum placeholder text simply represents any arbitrary content. In your case, of course, this would be the images.

I think putting the <iframe> into a container and then applying the CSS rules from below should be possible with Elementor.

.iframe-container {
    width: 480px;
    height: 300px;
    background: #ccc;
}

.iframe-dummy {
    padding: 10px;
    width: 460px;
    background: red;
}

.iframe-dummy h2 {
    margin: 0;
    text-align: center;
    color: white;
}

.iframe-dummy p {
    text-align: justify;
    color: white;
}

/* THE WORKAROUND CLASS (see AFTER example in HTML) */

.workaround {
    position: absolute;
    margin-top: -45px;
    clip-path: margin-box;
}

<h2>Before:</h2>
<div class="iframe-container">
    <div class="iframe-dummy">
        <h2>Annoying Title</h2>
        <p>Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua. At vero eos et accusam et justo duo dolores et ea rebum. Stet clita kasd gubergren, no sea takimata sanctus est Lorem ipsum dolor sit amet. Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua. At vero eos et accusam et justo duo dolores et ea rebum. Stet clita kasd gubergren, no sea takimata sanctus est Lorem ipsum dolor sit amet.</p>
    </div>
</div>
<h2>After:</h2>
<div class="iframe-container">
    <div class="iframe-dummy workaround">
        <h2>Annoying Title</h2>
        <p>Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua. At vero eos et accusam et justo duo dolores et ea rebum. Stet clita kasd gubergren, no sea takimata sanctus est Lorem ipsum dolor sit amet. Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua. At vero eos et accusam et justo duo dolores et ea rebum. Stet clita kasd gubergren, no sea takimata sanctus est Lorem ipsum dolor sit amet.</p>
    </div>
</div>

EDIT (in reference to a comment by the OP):

Can you show me a practical example directly for my website?

I took another look at your website and found that a suitable container already exists. Besides that, you can also omit setting position: absolute;. I have to mention that by not having custom class names or IDs, I had to fall back on what was there. I’ll come back to that later.

First, here is the required CSS:

/* Column containing Top sights in Bologna, etc. */

body.page-id-7215 .elementor-element-a8f0323 .elementor-widget-container > div:first-child {
    margin-top: -60px;
    clip-path: margin-box;
}

/* Column containing Useful Links, etc. */

body.page-id-7215 .elementor-element-0ca608c .elementor-widget-container > div:first-child {
    margin-top: -115px;
    clip-path: margin-box;
}

Targeting explanation:

body.page-id-7215 – is needed to not take effect on other subpages as well (unique page id)

.elementor-element-a8f0323 – class name of left column containing Top sights in Bologna, etc.

.elementor-element-0ca608c – class name of right column containing Useful Links, etc.

.elementor-widget-container – the widget container

div:first-child – the actual container of the <iframe> (the one we need)

Properties explanation:
I have already explained the properties before (see above).

Screenshot (CSS applied via DevTools):
https://i.imgur.com/tEusP11.jpg

Closing words:
To come back to what I already mentioned. Using .page-id-7215, .elementor-element-a8f0323 and .elementor-element-0ca608c is suboptimal, since these names can change, e.g. with a new installation, etc.