I'm entirely new to Lightroom so tx for your indulgence.
I started using LR to process pictures I take for photogrammetry. I import them raw, process them, and wish to export them to PNG. It doesn't look like LR CC supports exporting to PNG. Do you confirm or did I just miss something?
The cloud version of Lightroom (which is probably what you are using) cannot export to png indeed. For png export, you need the normal version of Lightroom which is called Lightroom Classic. It can export to many more formats than the cloud version can and gives you far more control.