Note that the original forum post talked about fragments.dbpedia.org which is a different API than the dbpedia.org pages that @timbl checked.
On the current dbpedia.org instance we only enabled https support on the /sparql endpoint to deal with web applications which need an https endpoint in order to use Ajax / CORS to get results from queries.
The DBpedia Association and OpenLink Software are currently testing a new database based on the new Databus technology which will soon replace the dbpedia.org content. With the new database content, OpenLink will also enable https access on all endpoints under https://dbpedia.org/
A demo is currently available on https://dbpedia.demo.openlinksw.com/sparql/
$ curl -I https://dbpedia.demo.openlinksw.com/data/Massachusetts_Institute_of_Technology
HTTP/2 200
date: Tue, 08 Dec 2020 15:25:52 GMT
content-type: application/rdf+xml; charset=UTF-8
content-length: 961476
vary: Accept-Encoding
server: Virtuoso/08.03.3319 (Linux) x86_64-generic-linux-glibc25 VDB
accept-ranges: bytes
expires: Tue, 15 Dec 2020 16:25:51 GMT
content-location: Massachusetts_Institute_of_Technology.xml
link: <http://creativecommons.org/licenses/by-sa/3.0/>;rel="license",<http://dbpedia.demo.openlinksw.com/data/Massachusetts_Institute_of_Technology>; rel="alternate"; type="application/rdf+xml"; title="Structured Descriptor Document (RDF/XML format)", <http://dbpedia.demo.openlinksw.com/data/Massachusetts_Institute_of_Technology>; rel="alternate"; type="text/n3"; title="Structured Descriptor Document (N3/Turtle format)", <http://dbpedia.demo.openlinksw.com/data/Massachusetts_Institute_of_Technology>; rel="alternate"; type="application/json"; title="Structured Descriptor Document (RDF/JSON format)", <http://dbpedia.demo.openlinksw.com/data/Massachusetts_Institute_of_Technology>; rel="alternate"; type="application/atom+xml"; title="OData (Atom+Feed format)", <http://dbpedia.demo.openlinksw.com/data/Massachusetts_Institute_of_Technology>; rel="alternate"; type="application/odata+json"; title="OData (JSON format)", <http://dbpedia.demo.openlinksw.com/page/Massachusetts_Institute_of_Technology>; rel="alternate"; type="text/html"; title="XHTML+RDFa", <http://dbpedia.demo.openlinksw.com/resource/Massachusetts_Institute_of_Technology>; rel="http://xmlns.com/foaf/0.1/primaryTopic", <http://dbpedia.demo.openlinksw.com/resource/Massachusetts_Institute_of_Technology>; rev="describedby", <http://dbpedia.mementodepot.org/timegate/http://dbpedia.demo.openlinksw.com/data/Massachusetts_Institute_of_Technology>; rel="timegate"
x-sparql-default-graph: http://dbpedia.org
content-disposition: filename=sparql_2020-12-08_15-25-52Z.rdf
strict-transport-security: max-age=15768000