You can't. The Gantry 5 menu system does not support that. You can add attribute to the link and list tag (top of that same page as your screenshot) but you can't add other attributes to the IMG tag.
that is, in this code that shows the menu item, there is no way to add attribute loading="lazy"?
<a class="g-menu-item-container" href="/my-menu" title="My Menu">
<img src="/images/icons/my-icon.png" alt="My Menu" />
<span class="g-menu-item-title">My Menu</span>
will there be such an opportunity in the future? because the speed test from Google tells me to do it.
I need to add this attribute for all images on the site, even for the site logo in my template (because if a person visits the site from a smartphone, he does not see the logo, because the logo is hidden in the menu and to see the logo, he must press the menu button)