If you don't wanna log out just to take a quick bathroom visit and not wanna be surprised with a sudden case of death do the following.
1- Activate console commands in the steam valheim launch options with... -console i believe?
2- open the console commands with F5 ingame and type in the following
3- devcommands
4- debugmode
5- exit the console commands and press the Z button

There you go, enemies will not notice you as you are in flight mode. When back, press the Z button again to disable it. This is the easiest way without mods.