The AGPL itself certainly has no rule against any startups using it. Where specifically does the prohibition you're talking about come from?
Here's google's policy on it. https://opensource.google/documentation/reference/using/agpl...
No it doesn't. The extra section of the AGPL that the GPL doesn't have explicitly says it only applies if you do modify it.
> Its universally banned not just startups.
You linked me to the rule that it's banned at Google, but still not to the source of any rule that it's banned at any startups.