So why is BTC up this last 24hrs and alts down? This I have never seen before, are people selling their alts to buy BTC? How can I find this out?
Are you sure this is your first time seeing this kind of thing? It happens a lot of times, and it's normal. It's hard to know if people are selling their alts to buy BTC as there is no tool to directly know the flow of money,
But you could try following the altcoin/BTC charts like ETH/BTC, LTC/BTC, BNB/BTC, you could get a clue of how the bitcoin price vs altcoin price moves over time
You could also look at the Bitcoin dominance chart. Higher BTC dominance = Lower altcoin price, Lower Bitcoin dominance = Higher altcoin prices (alt season)