So... the only "workaround" I found out is to allow the player to click a button, which will launch the game directly, in a new window, outside iframe.
However this approach is messy and confuses save data storage in the browser.
I cannot access the elements of the "iframe", because of "security" so there is no way for me to add clipboard permissions - the only way to do that would be to use code that could look malicious and I do not want to do this.
I'm not a web dev however, so perhaps I'm missing something here?