I’m having the same problem, game freezes after hitting the hotkey for inventory at the same time the game is processing something like finishing an event, leveling up, dropping an item… Last time, it froze here when trying to open the inventory right after the message for completing an event poped up on the screen. Had to close the game and start again.
It seems this is happening on consoles aswell, not only PC
Here is the link: PS5 game freezes when opening inventory - Console Bug Report - Diablo IV Forums (blizzard.com)