As I said Video Tag is being added to the dom by a third party js library I don't control, so I can't set the poster attribute myself.
I could through JS add the attribute to every video tag on the page, however this would still render it first with poster unset, and would still show that default video poster.
I found some other people with same problem, however this would have to be done somewhere in Cordova plugin I think :
https://programmersought.com/article/61143127917/