Actually, if you still had the older YouTube app, Google/YouTube just recently ended all support and functionality of this older version of this YouTube app.
So, no more YouTube app for iOS 9 and 10 devices, any longer!
You will need to access the YouTube Website through a Web browser, now, and logging in to the YouTube Website uzuning yiur YouTube login credentials.
Also, I would STOP using that well over 4-year old default iOS Safari Web browser, as it is too old, not secure and not safe to use to access the Internet, any longer.
There are virtually NO MORE third party Web browsers left for 8-10 year old iPads!
Available and more popular third party Web browser choices are pretty much GONE, now.
If you must use these old iPad models, here is what is left for still updated Web browsers.
Pickins’ are slim, now!
ALook Web browser ( A fairly new Web browser primarily designed for old iOS device versions, but is still available to newer iOS/iPadOS devices, as well )
Dolphin Web browser
Maxthon Web browser
TOR private browser
TOR + VPN private browser
Turbo VPN private browser
This is pretty much it for iOS 9/10 compatible, third party Web browsers today.
Use one of these more “up to date”, third party Web browsers from now on.
Accessing YouTube from ANY third party Web browser on this old an iPad will be much slower, BUT WILL work!
Good Luck to You!