It looks like a cultiver named Gryphon aka Pegasus. It's Latin name is Begonia x hybrida. I'm guessing the undersides of the leaves are reddish?

Probably a hybrid of Begonia heracleifolia and another species?

https://youtu.be/lmFML-auJLg?si=J7uPn4BhQb5fU1Z6

Jay has it correct. Gryphon is a popular thick stem begonia that is sold in nurseries.

I think the parents may be wollnyi and thiemei (or carolineifolia). There are a couple other crosses that preceded Gryphon that are so similar looking, such as 'Nancy Cummins' and 'Aussie Star'. There was another one that was simply named wollnyi x macdougalii (which is another name for thiemei). When PanAmerican Seed introduced Gryphon, it was patented or patent pending (cannot propagate it "legally" from what I've been told).

This was my old wollnyi x macdougalii. Gryphon seems to be much easier to grow.

'Nancy Cummins'

A few years ago, my Gryphon among many other begonias I was growing.

Thank you.