The short explanation
Televisions apply a lot of processing: motion interpolation, noise reduction, sharpening. All of it adds delay, which is fine for film and bad for games. Game mode turns most of it off.
Auto Low Latency Mode automates the switch. The source sets a flag, the display drops into its low-latency preset, and reverses when the flag clears. No remote, no menu.
Where you run into it
Without it, people play with 80 or 100 milliseconds of avoidable input lag simply because nobody pressed the button. With it, the switch is invisible and reliable.
As with everything else on HDMI, it has to be advertised to be used. ALLM is a capability flag, and if the flag does not reach the console the console does not set it.
How the DR HDMI 8K handles it
ALLM is a video flag in the DR HDMI 8K's EDID controls, alongside VRR: enable or disable it on top of the copied sink EDID. The OLED reports whether ALLM is supported in the EDID currently being presented, which turns “my TV is not switching to game mode” into a question with a visible answer.
Want to test your own HDMI chain?
The DR HDMI 8K is sold through the HDFury.eu web shop.