Today in ClickUp, this behavior is effectively “by design”: Guests can only start a direct message with members they already share a Chat Channel with, or if there is an existing DM thread. Simply sharing a task, List, or Folder with a guest does not make other workspace members eligible to appear in the guest DM people picker, which leads to confusing empty search results with no clear explanation.

Please enable guest to guest chat and guest initiated DMs (and, more broadly, let guests message relevant members) when they are collaborating in the same shared context (task/List/Folder), or provide an in-product flow to expand eligible recipients. At minimum, add clear UX guidance when search returns empty results (why it is empty and how to fix it), plus an in-product action to unblock guests (for example, create or join a channel with the needed members, or allow DM initiation based on shared items and permissions).