The on screen display will (I think) only change to ITVX if there is an
app which can be downloaded (automatically) and work with your TV or
other device.
We have a smart TV which works without any exterior devices. It has been
changed over to ITVX without any input from us
We also have a TV with an Amazon Firestick. That too has changed to ITVX.
Another set, in a bedroom, has catch-up provided by apps on a PVR. That
PVR apparently does not try to download new apps or versions. It's
showing all the content, but still branded as ITV Hub.
Your experience may differ, of course.