MediaWiki provides {{PAGENAME}}, {{SUBJECTPAGENAME}}, {{ROOTPAGENAME}} etc. for intelligent page name handling in templates and mass messages; the way these behave on Flow pages is unhelpful. E.g. [[{{SUBJECTPAGENAME}}/sandbox|your sandbox]] in an automated talkpage warning will normally point to the user's sandbox, but for users who have Flow-enabled talkpages it will point to Topic:<randomness> which does not match user intent and is unlikely to be ever useful (Flow pages do not come in pairs and do not have subpages).
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This is deliberate (T75409: Flow: magic words for page name in a post render as Topic:UUID but preview as Flow_board_name). Flow topics are actual pages, both technically and from a user point of view (e.g. they can be categorized by editing the summary).
The <randomness> part is a separate issue (T59154: Flow: Prettify thread permalink URLs/Titles (they are not human readable!)).
However, there is another task about providing a magic word specifically for this scenario, so I'm going to dup this into that.