YouTube version 19.20.2 is the last one available for iOS 14, but it has a bad bug where you won't be able to click on videos from the home or search screens. It is not simple to downgrade YouTube versions, unfortunately.
You need to do it through Trollstore.
Here are instructions on how to install Trollstore, with working links: https://ios.cfw.guide/installing-unc...ling-unc0ver-1
If you want, you can continue to install unc0ver through it, so you won't need to re-sign it every 7 days. But this isn't required.
Once you get Trollstore installed, first delete YouTube.
Then, go get this YouTube 9.09.4 IPA from here, by simply clicking on this link: https://huggingface.co/dangvinh77/uY...?download=true
Then go into your Files folder, navigate to Downloads, and rename it from "YouTube%209.09.4.ipa" to "YouTube 9.09.4.ipa".
Then go to Filza, navigate to the Files/Downloads folder, and click on that file. Tap Install on the top right. This will install YouTube 9.09.4.
If you are running uYou to block ads and download, make sure you downgrade back to 3.0.3.
This should fix it.
As I said, I also recommend installing unc0ver with it (though you can only use up to version 6.1.1 on iOS 14.0-14.3), so you won't need to keep signing it.