It depends on the circumstances of the market. Imagine an extreme hypothetical example, where one investor owns 90 out of 100 houses. And one new house is built every ten years. That investor has pricing power. They can essentially charge whatever they want even if it’s means some houses they own are empty (withholding supply). So: it depends on how fast new houses enter the market versus how much pricing power the investor possesses.

(In fact YIMBY doesn’t create an endless new supply. The idea is that it deregulates, facilitating a new supply where there wasn’t one before. That doesn’t constitute an endless supply, just a new one-time shift allowing a finite boost of additional supply.)

Another example: consider a speculative bubble. In a speculative bubble an investor can purchase a house, it can stay empty, there can be new supply coming into the market, but the forces of froth can outpace the force of additional supply, for quite some time. If they sell before the bubble pops, they profit.

Both these examples are of investors withholding supply, new supply coming into the market, and still profiting. Whether prices fall comes down to whether the downward force of new supply outstrips other forces that boost prices.