Yeah, basically this is terminating the trick some people used where they host a domain elsewhere but want to use an free personal GMail address as the "mail client" for it. Google sells their own domain email product, they'd prefer you use that vs. paying someone else.

And let's be honest here: GMail remains the preferred email client for almost everyone, for a lot of boring but very good reasons (mostly down to reliability and spam filtering).

Basically: people who don't like Google and don't use Google won't be affected and won't care. People who pay for Workspace hosting won't be affected, as those domains still work via Send-As. The people complaining here are in category 1, there are a handful of people (I'm one) in category 2 trying to help explain, and unsurprisingly there are very, very few people here in the actually impacted category of "mail client for external domain" users.