I am using Sharepoint Online (Office365). There are some default dynamic groups - "Everyone" and "Everyone except External Users", however I can only see "Everyone except External Users" when setting a permissions to some object. My goal is to share a site (kind of a landing page) where all external users would have access while the subsites have different groups and external users.
Found a solution, that worked.
Set-SPOTenant -ShowEveryoneClaim $true
Now "Everyone" appeared in the search and works as expected.