How to holster a weapon in Cyberpunk 2077?
- On PC, you have to double tap Alt.
- On Xbox, you have to double tap Y.
- On Playstation, you have to double tap triangle.
On all platforms, you can also open up the weapon wheel and select crossed-out weapon icon.
As mentioned in a comment you can also hold the weapon wheel button (ALT on PC, Y on Xbox, and Triangle on PlayStation) and select the crossed-out weapon icon to holster your weapon.