that's correct. on page 2 of the 24-pages release note, you'll find this:
Because this is a major Android platform update, note the following important information when updating to VideoOS 4.0.1:
● Downgrading to previous VideoOS versions is not supported. Once you update your system to
VideoOS 4.0.0 or 4.0.1, you cannot downgrade to VideoOS 3.x versions. However, you can
downgrade from VideoOS 4.0.1 to VideoOS 4.0.0.