Did you definitely install the nulled free version of Elementor and haven't updated it from inside WordPress?
Well I tried it again, this time completely disabling all elementor plug-ins, delete them, then re-install the nulled elementor 2.8.4 version cleanly.
Followed your instructions to connect a free template, connected via elementor page.
Installed the elementor pro 2.8.4, tried a free template, then use a pro block. It worked!
I'b be cautious though, NOT all pages or blocks worked (apart from the photography and magazine templates). I stumbled and got stuck when I clicked on some other pro blocks that I wanted but error message kept popping up.
Got to refresh the page and establish a new connection to get it to work again.
I tried some pages too, it works! Thanks so much!