This bitcoin halving thing happens around every 4 years which reduce the block rewards by approximately 50%. This is forseen as to help lower the supply of bitcoin into market which lead to increase of scarcity. So the problem is, will this block rewards reduction actually lead to a price increase due to scarcity or if the market has already priced it in?
The market cannot price in something that hasn't been in effect yet.
The deal is, when halving comes coins become expensive to mine, but the amount of coins being mined is only about 900 a day worldwide. It will take months before these new coins enter the market in such numbers that they impact the price. Imagine that there's 500k coins on an exchange and a large miner deposits 1000 coins a month there and he cannot sell below the floor mining cost which is somewhere around $50k. After 3 months he'll only have 20% of the supply of that exchange in fresh, more expensive coins, while the other 80% is "cheap" coins, minted with a floor price of 20k and lower (because that's what it was in 2023 and before).
The more post-halving coins enter the market the greater the impact of the halving on price, which is why bull runs usually start a year after.
