i3 Window Manager

This problem is rather obscure but I'll leave the solution here in case someone else runs into it and struggles to understand what's going on.

If you use Blender with a mouse that doesn't have a 3rd button, you can use either Alt or what Blender calls "OS-Key" to navigate: set it in Preferences ▶ Input ▶ Mouse ▶ Emulate 3 Button Mouse in Blender.

OS-Key is typically the Windows / Super key on a PC, or the ⌘ Command key on a Mac. In other words, for most of us, it's the magic i3 key.

Alt works fine. The problem comes if you want to use OS-Key instead in Blender and you have floating_modifier $mod defined in your ~/.config/i3/config file: Blender3 doesn't seem to mind sharing the key with i3, but Blender4 does.

If OS-Key doesn't work in Blender, try assigning floating_modifier to some other key, like Alt for example, like so:

floating_modifier $Mod1