https://wikidata.beta.wmflabs.org/wiki/Special:EntityData/Q64.jsonld results with the error:
Unsupported Media Type
The data format jsonld is not supported by this interface.
This happens despite it was announced on 16.10.2018 this format is now available on beta: https://lists.wikimedia.org/pipermail/wikidata-tech/2018-October/001344.html.
Primary suspect would be some change to the WMF wiki config, that unintentionally affected beta.
Test Wikidata (i.e. the deployment stage _after_ beta) is happily serving data as JSON-LD: https://test.wikidata.org/wiki/Special:EntityData/Q64.jsonld which makes the config accidentally changed theory even more likely.
Config should be altered to re enable this on beta wikidata.