Multiple Permission levels
Classic Sites provided 'page level permissions'. This is not a feature in New Sites.
The recommended workaround for users wanting to have multiple permission levels is to create linked sites with each site having the appropriate permission level.
Converting a Classic Site
When converting from Classic Sites to New Sites the approach is to make one copy of the Classic Site per necessary permission, delete the extraneous pages in each site, convert them, and then link them together in new Sites using the "New link" option under Pages.
For new Sites
For new Sites that need multiple permissions, users should create multiple Sites, set the permissions on each site, and then link in the new Sites using the "New link" option under Pages.
To end-users, the end result will look like one site, but they will not be able to view pages that they don't have permission to view. Please note that they will see a 404 error message if they try to open pages they don't have permission to view.
Multiple sites can be mapped to different subdomains of the same domain such as:
newsitesguide.pjrprojects.co.uk, newsitesguide2.pjrprojects.co.uk etc
I have created a linked Site (https://newsitesguide2.pjrprojects.co.uk/ ) which can be accessed via the 'Sub Site' link in the navigation menu.