Does anyone know how authority on passing these kinds of rules go, and if they are enforceable?

Is there some state/federal law that delegates power over some things to the municipalities/cities/counties etc that allow them passing ordnance like this?

It feels weird to me that this would not be a state / federal level decision, but maybe that's just my Finnish ass.

My understanding is that in typical Seattle fashion, this is a new legal requirement with zero funding or staffing to implement and enforce it. If you feel you have been wronged, hire an attorney and sue.

The constitution generally, at both the federal level and state levels generally has a clause like "if its not enumerated here then the next division down has the right to regulate it" hence why the feds regulate interstate commerce, but not state internal commerce. This usually stops at the county level, not the city level, but large cities are effectively their own counties so that distinction doesnt matter much.

Its enforceable in that the city has a police department and zoning rights. So they can force businesses out for violating the law, and they have they have the monopoly of violence within the city to make sure you follow their directions. But whether thats funded or practicable depends on other factors.