Just upgraded to 188.8.131.520 a couple of days ago. On Win 10. Each time i launch it i get a windows message asking if i want to allow this app to make changes to my computer.
I upgrades because i had been getting unsupporeted browser messages on multiple websites. I am still getting some, not as many but Yahoo Mail has been consistent since before and now after that upgrade.
You’re seeing Basic Mail because you’re using an unsupported Internet browser. Upgrade your browser for the full Yahoo experience.
I also note that when i X out the browser is takes about a minute before it closes.