I saw that there is $:/core/templates/social-metadata, I’m not sure if it is new, I only checked today because of a particular project.
Anyway, whenever I try to view-source or use checkers, it’s always failing. The meta stuff are not in the head section or anywhere on the site.
Is there a setting I missed to activate it?
P.s. I’m hosted on TiddlyHost.
I wonder whether it is a problem related to Tiddlyhost. The social metadata does exist inside the head tag in https://tiddlywiki.com/prerelease/ , but my tiddlyhost sites don’t have social metadata even though the social metadata information is filled in.
I just created a new wiki on tiddlyhost. 5.3.7. It produces meta data at the bottom of the header section. I don’t know if that’s what you mean by “working”. My TW file from 5.3.6 did not produce the meta data, so it seems to be very new (even though the tiddler was in 5.3.6).
<meta name="description" content="a non-linear personal web notebook">
<meta property="og:url" content="https://ratable-choking-94.tiddlyhost.com">
<meta property="og:title" content="My Social wiki">
<meta property="og:description" content="a non-linear personal web notebook">
<meta property="og:image" content="https://ratable-choking-94.tiddlyhost.com/thumb.png">
<meta property="twitter:domain" content="ratable-choking-94.tiddlyhost.com">
<meta property="twitter:url" content="https://ratable-choking-94.tiddlyhost.com">
<meta name="twitter:title" content="My Social wiki">
<meta name="twitter:description" content="a non-linear personal web notebook">
<meta name="twitter:image" content="https://ratable-choking-94.tiddlyhost.com/thumb.png">
</head>
That’s weird. I can see it working on yours.
In the 5.3.7 tiddly I created (without edits), it isn’t showing either.
Hmm… what could be causing it. 
Maybe because it’s not public? I can’t view it.
A good suggestion!
Tried it but still the same, but it led me to test something unique to TiddlyHost: detached core.
I created a new test site with detached core
https://testmetadata.tiddlyhost.com
Result: so social-metadata
Then I created with attached core
It works.
I’ll file a report on TH’s git.
Filed a report here:
Thank you everyone! 
It was also filed here by Leilei:
I suspect Tiddlyhost can’t do anything about this.
If you edit $:/core/templates/social-metadata in some small way, perhaps just adding a space to the end, save and reload, then the meta data will appear in the source.
I tried that, and it worked!
Thank you very much!