@Bruno Aleixo,
Thanks you for bravely wading into this conversation about "Everyone except external users" being removed from the visitor group. Could you please explain the reasoning for this?
We have alot of scenarios that have a public/private component where we use an O365 group with Teams to manage the collaboration portions but want to allow the entire organization to view the information on the site. Project work is a good example. We want the communication and edit ability restricted to the Team, but want to allow anyone to view the documentation or other work products. We're using the same model for our User Group.
I'm very frustrated with the lack of documentation around some "features" of the modern sites. As site owners & admins, we're going to expect the sites to work as usual UNLESS YOU TELL US OTHERWISE. This isn't documented anywhere. The page on Sharing and Permissions in the SharePoint Modern Experience would be a perfect place to state that if you invite "Everyone except external users" to the visitor group, SharePoint will clear out the group eventually and then explain why.
FYI to anyone following - another tidbit on modern sites and permissions, as owner of an O365-enabled site, you can only make site-level columns that are text-based such as string, number, date, choice, etc. In order to make a complex site column like lookup, people or managed metadata, you must be added by name to the site collection admins.