It sure seems to be. Look at the red X's and green checkmarks in the comparison: https://element.io/pricing There are different opinions on what Open Core means though.
Some of their bridges (e.g. Teams bridge) aren't open source. But those are separate software projects. AFAIK synapse and element aren't open core but fully open source (with apache licensing).
I'm comparing Element.
> and so isn't Element
It sure seems to be. Look at the red X's and green checkmarks in the comparison: https://element.io/pricing There are different opinions on what Open Core means though.