Yes, you're able switch off specific team member's availability easily.
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We call this the "Availability Mode". Please follow the below steps to activate.
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Click on the Gear icon to view the Settings page and click on Users & Teams which will be directed to the page shown below.

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Next step is to click on the 'Availability' option.
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Select the team member, and click 'Online', the team member's availability will automatically be updated and shown as 'Offline'.