I have been having thiis problem too. I’m running Windows 11 on a Dell laptop with Core I7. It appears to be hardware dependent.
I opened a support ticket. Was asked to try other browsers and got the same effect in multiple browsers (DuckDuckGo, Chrome, Edge). Then tried other devices and the videos all played fine on every other device of mine: (Phone – Samsung and Google, Tablet – Lenovo, all of these are Android devices; also works perfectly on my Linux Mint laptop. So I do TAC on my Linux box now, occasionally I’ll run it on my Win 11 again and it does work intermittently, if I’m switching from lesson to lesson and just launch a single vid it seems to work typically.