When your Youtube app says tap to retry it's likely your device has lost the internet connection to the WiFi signal.
Sometimes you need to turn off the WiFi connection on your device and turn it back on or sometimes you may need to completely restart your device for it to work.
Your internet connection could also be down but if not usually restarting your device with the Youtube app will fix the issue.
If not then you may need to reinstall the Youtube App to fix the issue or Youtube could be having an issue themselves.
But most times it's caused by the internet connection dropping and you need to restart the internet connection on your phone or device but turning WiFi off and back on.
That usually fixes the issue for me.