The YouTube TV app not being available has been the case for many months, ever since the contract for Roku to carry the app ran out. As you now know, removing the app from your Roku device makes it no longer available for you.
You have also happened into the middle of an unrelated issue with the YouTube app. YouTube app version 2.20 is having issues, particularly with some 32-inch TCL Roku TVs. Other sizes and brands may also be impacted, but these have been confirmed.
YouTube app version 2.21 works on many different Roku device models. Google determines which versions of their apps, including YouTube, are available to which Roku devices. Actually, all developers determine this, but for YouTube, it's Google.
Once Google decides to push an update to 2.20, or make 2.21 or another version available to the impacted devices, things should go back to normal.
As a temporary workaround, some of the channels you watch with YouTube TV may have their own standalone Roku app. If so, you may be able to authenticate against YouTube TV with the apps.
Roku Community Streaming Expert
Note: I am not a Roku employee.
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