The updated version of Sin released by Nightdive breaks the way the game input functions. Normally, you can press the minus and plus / equals key to make the screen size smaller and larger and then hide the hud.

In the normal game (without the update) when the game area is fullscreen, pressing the plus key one more time also removes the hud (a basic functionality that was in a lot of games from that time).

However, Nightdive somehow broke that ability and the hud can no longer be disabled by pressing the +/= key. They did the same thing in the Blood remaster. They provided hide hud menu options in the Blood - Fresh Supply menus, but they broke that too because any time you load a save or start a new level with the crosshair disabled, it turns on the hud and crosshair and ignores the menu settings.

Please fix that (in both sin and blood).

For the time being you could bind scr_showhud to a key from the console
example:

bind o "scr_showhud 0"
bind l "scr_showhud 1"

This should do the trick.