I seem to remember this was an easy report in UA (GA3).
In GA4, it seems impossible. There is no dimension called Landing Page. The documents say use "Session start page" which of course does not exist.
I can use Landing Page + Query String and export to filter out the known Advertising stuff - but no "Export" option for Custom Reports (aka Explorations).
Plus when I try to change the date range, there is no option available - despite the docs that say there is an export button in the right hand corner.
Maybe this is a set of noob errors - but it seems to me that this thing is still not ready for prime time. Either that or it has been dumbed down sufficiently to make it nearly impossible to get useful data out of it?