anything *.google.com ?

Yeah, pretty much it.

Is your default container the one with the Google cookies?

I personally haven’t found a way to make a container default. I just have a separate container for my Google accounts and other accounts connected to it.

Thankfully I found the solution to my problem by using Temporary Containers

Also, is there a preferred way to create a Firefox account? I don’t want to enter my personal email, and adding a disposable email may lock me from this account if it asks for verification later on.

Yes, I did start using PIped and Invidious on my browser and installed Newpipe in my phone. Tho there are some drawbacks, it is much better than using Youtube directly after I heard about them planning to block adblockers and removing recommendations for signed in users with watch history off.