Be very careful when Groupifying a SharePoint site.

Summary: Check and Reset the Sharing setting on the SharePoint site once you groupify SharePoint sites. It has been reset to allow external sharing!!!!!

Recently I upgraded approx 2000+ classic SharePoint Site Collections to modern Group based Sites.

About 80% of those Site Collections had external sharing disabled:

That shouldn't be a problem because the documentation clearly states that

Edit Dec 18 2023 MS has updated the documentation to warn about this issue

HOWEVER, that might have been the case once, but it is no longer the case !!!!!!!

Step I used to verify:

Create a new STS#3 site

Check that sharing is set to "Only people in your org"

Go to the site colleciton

"Connect to a new M365 Group":

Keep the defaults

Check the Sharing settings for that site in the SharePoint Admin Center:

As I don't know whether the documentation is correct and the code that is doing the groupification is buggy, or the documentation is wrong I have created an issue in the documentation, hoping to get this resolved before anybody else gets tripped by this:

Adding a Group to a Site DO change external sharing and exposes internal content :-( · Issue #9386 · SharePoint/sp-dev-docs (github.com)