afloat and at any time can just allow it to crash?
There are lots of indicators of economic health, and they are all looking rather bleak. One of them is history: every use of unbacked paper money has led to a collapse within 40 years. We are now in the 47th year since Nixon abolished gold backing of the USD in 1971, but this is also the first time in history that printing counterfeit money did not require an actual printing press.
Yes, there is a shadowy group with the sole purpose of pouring counterfeit money into various markets to keep up the appearance of normality. The indicator of stock health is price divided by earnings, usually called PE. Normal ratio is around 15 and when it gets up toward 30 we start talking about a bubble. Right now it is 24.
https://www.multpl.com/