MediaWiki can be configured to display the signature button in the editor in additional namespaces (in addition to all talk pages) using $wgExtraSignatureNamespaces. All the common editors (built-in wikitext, WikiEditor and VisualEditor) respect it. I'm not sure what exactly you're requesting, though, can you clarify?

Insert > More > Signature is grayed out on that page.

@ThurnerRupert Could you discuss the issue on the local project, first to get a consensus to enable the signature button to the Benutzer/User namespace, and secondly to ask if other namespaces would be needed?

@ThurnerRupert ping?

@Dereckson , now i know a wish to notifications: it should include phabricator mentioning my name :)

for the issue itself i am unable to decide now, i thought it works differently on a technical level. it needs a ticket here despite it would only be a configuration change?

Any configuration change should be discussed on the local project to get feedback from the community as a whole.

For example, on fr.wikipedia, they rejected such idea and either suggested projets to use discussion namespaces for their main talk page.

the discussion is clear, but does it need a ticket or we close it?