I dont really think its in a ready state in 4.25. I see lots of active development of this stuff on the master branch on github in preparation for 4.26.
I have tried the master branch a number of times in recent weeks. Sometimes some stuff works, but I dont think everything is done yet. 2.5 and 3D stuff is currently hidden as far as I know, but there was a period some weeks ago when I could still see some 2.5D examples.
Some stuff can still be found within the ShallowWater plugin, but more recently they have now added an experimental plugin called NiagaraSimulationStages.
And within that plugin there are a few systems included that I can get working at this stage.
For example, when you have the show engine and show plugin content flags ticked in the content browser, there are some Flip Systems to be found. I was certainly able to get the one called Flip_System working by dragging it into a scene, and it is to be found at /NiagaraSimulationStages Content/Templates/Liquid/2D/Emitters/