All modern electrical installations have Ground, Neutral and Phase (1, 2 or 3 phases). Normally in a house they are 1 Phase, Neutral and Ground (monophasic). In Spain 220V of alternating current.
We could say that the neutral is grounded in the power plant generator.
If you measure with a multimeter the voltage between the phase and the neutral and the phase and the ground is exactly the same.
If these measurements are different, it may be an indication that your grounding installation is faulty and you could lose protection against electrical shunts.
Grounding wire is for user safety.
If an electrical appliance, washer,… has a shunt from the phase to its chassis, the current that must flow from the phase to the neutral and vice versa, since it is alternating current, return in part to the wired ground and the differential switch in the panel of the the installation will detect that the input current (L) differs from the return current (N) by more than 30 mA and will trip the general switch of the installation.
If You do not have a ground wire, the current derived from the chassis does not flow to ground wire and the differential switch will not detect a difference in input and return current until you touch the appliance with your hand and the derived current passes through your body. At that moment, the differential switch will save your life when more than 30 mA pass through your body.
The switches cut and connect the phase that goes to the bulb and the neutral is always present on the other terminal of the bulb.
If the Neutral is not in the switch box to power the device, you can look for it in the junction box that is usually higher on the way to the bulb.
When you want to use a device without Neutral, what happens is that the device changes the mechanical relay for an electronic switch with an adjustable high impedance (triac or thyristor) and uses the neutral that comes through the resistance of the bulb to feed the electronic circuits of the device.
These dimmers require that the bulbs be of the incandescent type, allogen … so that the neutral can reach the device.
If you are going to use led type bulbs, which have an electronic circuit, it must be of the dimmable type and a capacitor may be necessary in parallel with the bulb so that part of the neutral current can pass through the capacitor to the device. There are certificates like this one from fibaro, but if you search on the internet you will still find cheaper.