Modern Sites ?

Modern site are showing up in SharePoint 2019 and have been around since 2016 in SharePoint Online

Modern Site Challenges

Managed Comments on News Pages

currently limited to on / off – or manage via api (2/2019)

https://www.vrdmn.com/2017/07/working-with-page-comments-rest-api-in.html
https://sharepointmaven.com/2-ways-to-disable-modern-page-comments/

Save View Instead of Creating / Changing View Via Old UX

group by promoted state only via new UX (2/2019)

New Modern Web Part List

https://wonderlaura.com/2016/10/17/new-modern-web-parts-full-list/

Tabbed Forms (PowerApps)

https://wonderlaura.com/2018/01/03/powerapps-tabbed-sharepoint-form/

References

https://sharepointmaven.com/how-to-bypass-the-new-modern-team-site-page-experience/

https://www.microsoft.com/en-us/microsoft-365/blog/2016/08/31/new-capabilities-in-sharepoint-online-team-sites-including-integration-with-office-365-groups/

https://wonderlaura.com/2016/10/17/new-modern-web-parts-full-list/