I did some testing and can confirm the latest Teamviewer for iOS (on the brand new iPad pro 11" or an iphone XS) both cannot play remote audio from a Windows 10 machine - but with an older iPad or iPhone (with the same exact version of TeamViewer connecting to the same PC) the remote sound comes through.
I read this thread, https://community.teamviewer.com/t5/TeamViewer-General/No-sound-from-remote-computer-worked-previously/m-p/10880#M5911, but nobody had narrowed it down to this case (reproducible).
So, I'm trying to find out how to report the bug to the company - as the user of the free version, I cannot open a ticket.
Thanks!