The problem worked itself out.
My kid decided to turn off the TV & do some drawing.
I was looking-up ways to bypass the log-in (using my computer) & couldn't find anything that would help, but I decided to turn the TV back on & go back into YouTube to check the sign-in message that was coming up.
And that time, I was able to get right into YouTube without a sign-up screen popping up. Hopefully it was just a glitch.
We have a Samsung Crystal UHD TU8000 (2020).
I was going to checkout the SmartTube app (thanks for the mention), but reading about it (https://smarttubenext.org) I may have a problem since our TV has a Tizen OS & not Android OS.
But I contacted smarttubenext.org to find out if anyone can help me.