It's a totally separate tab that opens. It's got nothing to do with what you use as your homepage.
I'm on gentoo. I have to update chrome manually. I updated it. On update I _never_ get a "what's new" page. I've had this profile for more than a decade so I have no actual idea why, but, I can absolutely tell you, I do *not* get one. After update it started consuming all my bandwidth. This use did not show in it's task manager. I have a metered connection. This is a problem for me. I worried it was a compromised plugin. I had to spend 10 minutes in Firefox discovering why chrome was doing this then going to the configuration and disabling this.
This was a disappointing experience. I'm sorry you feel differently; other than stating the obvious, I seriously have no idea what you and the other corporate defense squad members are trying to achieve with this gaslighting nonsense.
Note that this package and update is actually not maintained by Google at all, it's done by Gentoo: https://wiki.gentoo.org/wiki/Project:Chromium/How_to_bump_Ch...
I hate to be an apologist for anything but I think you are pointing fingers in the wrong place. The Google-official releases use the built-in automatic updater and do show What's New. This is a Gentoo release and they chose to do their own thing for updates.