Yes, that does make a difference and no, it’s not.
An autocomplete list is most likely generated based on statistics and contains sites that are being _used_, and an allow list is moderated and contains sites that are _condoned_.
Yes, you can continue to use Vanced for now, if you already have a working APK or can procure one. But with no updates coming, it's only a matter of time before YouTube make breaking changes and it stops working. I would guess 6 months to a year, based on how often I've needed to update in the past.
The Mekong, the usual river that comes up when it comes to water rights, originates in Qinghai province, not Tibet. Any other rivers originating in China and flowing through VN would be even further east.
You might be confused because the Mekong (along with numerous other rivers) originates on the Tibetan Plateau, but that's a geographical feature which is vastly larger than Tibet itself.