Source: Jurrie Eilers, sticky blogposts sidebar and sticky widgets on the blog index.
https://www.zelfkennis.nu/blogboek/

@media (min-width: 981px) {
.et_right_sidebar #sidebar, .et_pb_widget_area {
    position: fixed;
    right: 5%;
    top: 21%;
	max-width: 30%;
}
}
Code language: CSS (css)

Of een 2e manier, ook van Jurrie. Werkt fantastisch in chrome, firefox en safari.

.stickthis {
position: sticky; 
top:40px;
}
Code language: CSS (css)

Alternatives

• On the advanced tab of a Divi element, set Position to Fixed.
• Plugin “Sticky Menu (or Anything) on Scroll