It is fuzzy as there is no exact answer to this question I am afraid.
It has always been the case though even prior to the internet (yes there was a time) that a target speed was always under 3 seconds to display to a user the results. That magic figure seems to also hold true today.
Now the technical OCD in me thinks 3 seconds is too long and the closer you can get a page to load to < 1 second the better. However, I have never seen any proof that the difference between a site loading in 3 seconds or 1 second has any effect in rankings.
There is though something else to bear in mind. Sites that load faster get more pages crawled when google bot comes to have a look. Each visit they will index more pages the faster your pages load. This on its own should be enough to persuade anyone into lowering the page load times.
Images are always a quick win for lowering page loading times and so many sites I visit I see huge images re-sized in CSS to fit. This is a huge no no for mobile users and your just sucking up their available data usage.
So in short < 2 seconds is now my new target in 2020 but I try and get far quicker results than that where possible.