Surprisingly, I don't think you can do transparent headers with Elementor Pro 2.x YET.
This would require Elementor to have set two colors for menu items – one for the transparent header and the other for sticky headers and regular headers such as in archive pages.
I would love to be corrected on this issue. But I don't see it yet.
Since I love a transparent header, I simply use Astra Pro's feature for transparent headers.
I had the same question. I searched for the word “transparent” in Elementor's docs – zero results. I am quite sure they do not have this capability yet.
Transparent headers are available – with a little bit of a work around, see here https://igniteweb.design/blog/elementor-header-transparent-sticky-scroll-changes/