There are different tools to estimate and get reports from, but most of them are paid version. Semrush does have a kind of test version.
If we have a look at Similarweb, the results are not that satisfying, but you can get an idea. So it is about 25% of the traffic based on organic search, based on Similarweb.
Thanks for that Jay... 25% is pretty great... I'm sure that'll increase over time as the database fills up.