Welcome to our Community and thanks so much for your first post - I was sorry to understand that you've been having some issues with viewing YouTube via your set top box recently. As our VIP @japitts has advised, the YouTube channel was removed a while ago now to free up channel listing spaces.
There should be no reason as to why it won't load up via the apps section though. I have located your account from your forum information and can see that you have 2 boxes - are you having issues viewing YouTube on both of them?
We can see that one box was last rebooted around a week ago, the other was rebooted around 72 hours ago. We can see that your hub has not been rebooted for 44 days. Please do reboot your Hub at your earliest convivence and see how you get on.
44 Days uptime and you've had to re-boot your router? Yikes...this is why i use it in Modem mode! Record uptime for my own equipment has been 404 days without errors on my Pi-Hole DNS device, 386 days for my enterprise Gigabit network switch (Layer 3 managed) and 275 days for my WiFi AP (a third party Router in AP mode) and really only rebooted them as a matter of course. That's a bit worrying! Is your router getting hit by strong sunlight or enclosed in any way, or up high? Often the main reason mine goes down and reboots every so often is a firmware update!