Linked Card feature was added at https://github.com/wekan/wekan/pull/1592

With Linked Card feature, it's possible to create new board as dashboard. At dashboard board, you add new card Link, and there link to some card at other board, so you see realtimes changes from all those cards at dashboard board.

Search is for searching card, to be as linked card, I presume.

There is also Linked Board, but I'm not sure is it useful.

Related PRs at https://github.com/wekan/wekan/pulls?q=is%3Apr+is%3Aclosed+linked+card+

Related issue https://github.com/wekan/wekan/issues/5550