ALLM might be a "HDMI 2.1 feature" but its been supported on non-2.1 HDMI TVs and receivers for a while.
VRR might be useful to many, again non HDMI 2.1 GPUs have supported it as well as 2019 LG but receivers havent, making it harder for users to connect up GPU/receiver/TV.
4K/120 might be straightforward for a TV to implement but PCs are just about happy at 4k/60 and next gen consoles may catch up with that - so 4K/120 wont be that commonplace despite everyone thinking they need it.
Its GPUs and receivers that need to announce support - TV manufacturers have been poor not adding it to 2020 TVs after LG added it in 2019,