The biggest secret is that banks buying crypto a lot not gold the gold is for retail buyers.
How do you know if it's such a huge secret? Do you have a private channel where bankers talk to you about their plan or something? I don't know, it sounds like you're just seeing what you want to see. It doesn't make sense for them to abandon gold even if they're going to buy more crypto, because it has a good record for a hundred years now. Most people still don't think crypto is as safe as gold, so there's a huge chance they'll just withdraw their money from the bank if they know about this.
No offense but I think OP doesn't know what he's talking about or he's telling us about his dream.
According to several reports from the World Gold Council, central banks have increased their gold holdings in recent years due to increasingly volatile geopolitical situations. In particular, the PBOC has accumulated an unprecedented amount of gold in recent years to prepare for China's de-dollarization idea. So, without concrete evidence, the claim that central banks are selling gold to buy crypto is a BS claim.
Crypto is just a speculative market, banks will not need such risky assets.