This appears in previous versions and remains as of Beta v.1.17.7.
The wall trick is an exploit that relies on enemies detecting and attempting to attack the player through a thin wall, so no damage is dealt. As long as the player doesn't move too far, the enemy won't try to move around the wall to actually attack and deal damage. The player may use this to their advantage by quickly moving out from behind the wall to attack the enemy between enemy attacks.
This exploit is particularly useful in the Motel, Bunker Alfa, or other zones with walled structures. It appears that enemies are programmed to close the distance between themselves and the player until they're within a certain attack range. If a barrier is thin enough to satisfy this range, the enemy AI will not attempt to change position, despite the fact that such a barrier blocks attack damage. Notably, player attacks cannot cause damage to the enemy while enemy attacks are blocked.
From the description above, the wall trick may seem useless at first, but it can be used strategically by quickly moving to strike from behind the wall and then quickly returning to a safe position in between enemy attacks. This is especially helpful for deadly enemies like Frenzied Giants, allowing players to defeat them with melee weapons alone.
Theoretically, using the wall trick could allow players to defeat any kind of enemy while taking no damage and only requiring the simplest weapons. However, it's not a cheat and does require a degree of skill. As indicated by Kefir! themselves in an animated promotional video, the wall trick complies with the lore as a means of exploiting the stupidity of zombies. To use it correctly, the player must account for the number of enemies on the other side of the wall, the range and attack speed of their weapon, and the enemy's attacking speed. Great care must be taken with both timing and positioning.