One big piece of the puzzle is inflation. If we continue to see it cool off around the world, central banks especially the U.S. Federal Reserve might start lowering interest rates. That shift would make borrowing cheaper, encourage more investment, and usually boost the appeal of riskier assets like stocks and cryptocurrencies.
Another major driver could be institutional money flowing into the space. If heavyweight firms like BlackRock or Fidelity deepen their involvement whether through tokenized assets, crypto ETFs, or building out blockchain infrastructure that kind of endorsement could bring in serious capital and boost confidence across the board.
As you said, a single event can't trigger a bull run but will involve a lot of such events where either the governments try to back cryptos or major institutions start investing people's money into cryptos(which already is happening with a lot of major firms). I also consider mass adoption as a key factor for the upcoming bull run but it is adversely affected by all these events.
Right now, the governs play a major role. Any supporting bill from governs will drive people crazy about cryptos and will catch their attention. Nowadays, I can also see a lot of centralized providers promoting cryptos even though they report everything to the governs and try to regulate the transactions.
If reserves start lowering their interest rates then they also might have to lower the interest rates on fixed deposits or any other means of deposit which will force people to withdraw their money & invest it elsewhere. I don't think the reserves will take this kind of a move as they might end up giving a lot of loans but there will be no deposits to back those loans.