Assuming you are using KDE. I had the same issue, this is a KDE Bug starting with Plasma 6.1
Fix: Go to System settings > Session > Desktop Session, [select] ‘Start with an empty session’ and reboot. You can switch back to your preferred setting afterwards.
Source: KDE Hangs on Shutdown, Restart and Logout. Black screen [SOLVED] (Page 2) / Applications & Desktop Environments / Arch Linux Forums
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