The back-to-top distance is hardcoded in all.min.css with the css property bottom: 30px; and right:30px .
I know this can be achieved with aditional css, but this is adding other layer to the onion.
Now, much of the social sharing buttons plugins are setting the buttons bar at the bottom of the screen when in mobile, each plugin had their own height and, in the most cases, they are covering the back-to-top button.
This can be avoided making the bottom and rigth css properties selectable in customizer (in px or %) and then don´t need to add aditional css.
If I don´t resolve this then I can´t make a new ticket. So I will this open as a reminder and make the new feature request here.
Now Google Insigth has a new metric called Cumulative Layout Shift (CLS) that relies in changes in the layout of the rendered page when a element changes in the viewport.
Whit lazyloaded images this occurs, and the solution is to put sizes in the parent div container of the image, so the space is “reserved” to the real image when is loaded.
But the parent div cointainer may not know what the image size is, so we need a catch-all size. This may be acomplised with a width: fit-content css property.
For example, you can view it here: https://intersindicalrm.org/spublicos/jornada-laboral-especial-112/ in the <div class="featured-image page-header-image-single "> I have added the css property with a function in the functions.php of the child theme.