User can tap their profile to locate a Time-Off Request Button. This will notify HR of the request to approve/decline, which will notify the user.
In addition to this, an HR Dashboard separate from Spaces/Lists would house each employee's requests and time-off history for quick evaluation.
Unlike spaces or lists awkwardly serving this function without privacy, a dedicated HR Dashboard connected to employee profiles and requests would provide privacy of requests between colleagues.
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To add: I can imagine Click-Up having Spaces & Lists for project management, then an HR Dashboard with advanced User Profiles for managing employee time-off requests, history of approved/decline requests, and private notes.