it's very strange, because it works with W and L, but with m and nf it doesn't work, it never iterates

Replace parameter M with MM. M is a special reserved multiplier. I see 3 different currents in I(VDD4) this means that ngspice is correctly iterating the MM parameter. Transistors have attribute

mult={MM}

I don't understand why it doesn't work for me, I changed to MM and I still don't see the iterations

Here the working schematic. You see the 3 values for [m] in the graph.

can you look at the mean commands in the simulator? do they change with each iteration? is that if you look I have a line that saves the variations of that with respect to the change of M, that file does not change with multiplicity or fingers but with W and L, yes

Of course measured delays do not change. If you multiply the whole circuit you will have the same timings. Add some fixed capacitance on the inverter outputs and you will see a difference

Do you know if this technology is 130, is it overloaded with a very large W? I wanted to characterize that