[Android Apps and Games] Timmmmaaahh!:
This usually happens if something on your end is blocking YT from accessing the interweb thingy. Got an adblocker running?

Spoken in the true spirit of XDA; thank you. Let's get back to your original inquiry:

This is actually difficult to answer and I understand your confusion. Let's face it, the first posts are pretty messy, confusing and out of date. It often raises more questions than it answers to new users so I would definitely not consider it spoon-feeding either.

In theory, YouTube (OYT) should be

replaced

by Vanced YouTube (VYT) in case of choosing the root version as it has the same package name. It has often been recommended to

remove

OYT first to then install the root version. The problem here is that there have been many ways of installing VYT, which brought several installation scripts to the table that all worked in a (slightly) different way. In case of the Magisk module, leaving OYT before installing seemed best practice as I read several reports of people not seeing any YT after removing OYT and then installing the VYT module. Many of those solved this problem by removing the module, installing OYT and installing the VYT module again. But it's not 100%, sometimes it did work just fine by uninstalling OYT first.

Still with me? lol.

The original legacy root installation of iYTBP (original name of VYT) required you to replace the apk in its app folder and setting permissions with a root enabled file manager. In this case it was easier if OYT was already installed but again, it worked by manually creating the folder too and neither ways always worked 100% (probably device related). Later there were scripts to flash in recovery that did this replace/install for you.

The current SAI method only adds to the confusion. As the guide on the vanced.app website doesn't state anything about it, VYT installation will probably work with or without OYT installed and likely with a higher success rate compared to older installations as [MENTION=8983809]Team Vanced[/MENTION] has matured its scripts over time. Ignoring the MIUI-SAI incompatibility issue for a second.

With the non-root version it's dead easy: it doesn't matter at all because it's a

different

app. The package name is different so your system doesn't consider this related to OYT at all. That's why you need MicroG if you want to connect your account. Both OYT and VYT can run alongside each other but I would consider uninstalling/disabling OYT anyway (before or after installation, doesn't make a difference) because you simply don't need it anymore.

About auto-update: updates via Play Store to the root version of VYT will actually update it to OYT. That's why some complain about losing VYT functionality all of a sudden. This is easily solved by selecting 'uninstall' in the Play Store page as this removes the OYT update, reinstating VYT.

Edit: I have been told this detach method is completely effective. I mean, who's to argue with this review? ;)

TL;DR

Does Vanced require the default YouTube app? Yes and no :p

Should I keep auto-update on for it? No, never!

You need it if you're not rooted, but don't need it if you're rooted? It's actually the opposite but there's no straightforward answer in case of root version.

Did that make any sense? Haha.. I'm not even sure myself! Feel free to ask more questions and if anyone spots a mistake, please let me know so I can correct it.