Sometimes ago, it was working properly without doing any explicit configurations like the below in our sharepoint2016 site(https://) But now it is failed to display the external site link content (https://) from another domain.
Part of fixing, have done the below things, but still not able to resolve the issue.
i)added this (WebPartPages:AllowFraming runat='server') inside custom master page. ii)"Permit contributors to insert iframes from any external domain into pages on this site" option is selected under Site Settings > Site Settings > Site Collection Administration > HTML Field Security.
Do we need to do anything else or this feature(displaying iframe is depreciated in sharepoint)..?