Low interest rates primarily means low interest rates for the government, which the central bank implements by simply buying their national bonds at rates much lower than the rest of the world would tolerate. This sucks up the supply of low-risk low-reward debt that would normally attract a lot of investors. With that supply all bought up those investors are then forced into higher risk instruments like equities, which pushes up the value of stocks (not coincidentally, the kind of investment that Congress tend to have a lot of). High valued equity means greater rewards for startup investing, and so capital diverts there.
So it's all based on pushing investors around against their will, more or less.
Sure, I get that: when zero risk returns are low (or zero), investors must take on more risk.
I don't think this explains why the "good times are over" however. I think that is more related to supply / demand. Supply was low for a while as tech was seen as a dead-end in the early 0s due to outsourcing. In the mid 2010s the opposite was true - tech was seen as essentially the only viable career so lots of people went into it. Now we have the perfect storm of natural oversupply and the threat of AI.
I think the situation will eventually reverse but it will take quite a while.
