Electrical – Transistor as a switch in active or saturation region

But again at the same time "Vce under 0.2V" means there is saturation which means Ic must be maximum

The "theory" is just a "rule of thumb" when turning a BJT on to act like a switch. The current that flows is still dependent on base current and collector voltage: -

Once the collector voltage has lowered beyond a point the BJT leaves the "active" region and enters saturation where it is "like" a base-current-controlled variable resistor. See the different rising slopes extending from the origin - if you approximated these to straight lines each has a V/I ratio just like in a MOSFET: -

Of course it can be really confusing the way that MOSFET's saturation region IS NOT the BJT's saturation region but the reason is clear if you consider that for a BJT it is saturation of the base whereas in a MOSFET (or JFET) it is saturation of the DS channel - two totally alien effects but called the same thing.

EDITED SECTION

I've added this because some internet pictures of a BJT's operating characteristic are incorrect. See below at an incorrect diagram of the BJT in saturation: -

There is NOT one line representing all base currents - each base current graph is individual and not "merged" as per the incorrect picture above.

Real answer is you don't. Hfe varies by temperature, part to part variability, collector current and voltage. Since you can't know what Hfe is at any given time, you make a circuit which is robust to the variations of Hfe.

1. Start by using a typical value and determine the component values (resistors) and bias points in the circuit. Then check to see if you are in the operating envelope of the transistor (power dissipation, max currents, max breakdown voltages). Check the bias points to ensure you have adequate headroom for your AC circuit (ie you can achieve the gain you need at the signal level you need and you are still in the linear region).

2. If you are, then without changing the component values, change the Hfe for the worst value and check the operating envelope again to see if you are still OK. Check the bias points to ensure you still have adequate headroom for your AC circuit (ie you can achieve the gain you need at the signal level you need and you are still in the linear region).

3. If you are, then without changing the component values, change the Hfe for the best value and check the operating envelope again to see if you are still OK. Check the bias points to ensure you still have adequate headroom for your AC circuit (ie you can achieve the gain you need at the signal level you need and you are still in the linear region).

4. If you are, congratulations, you've accomplished something called robust engineering, and you can be sure if you get a random sample of (the same type) transistors, that the circuit will work properly.

5. If you fail along the way, then either find a different transistor that is better suited to the operating envelope, or revise the component values to better meet the circuits needs within the transistor's parameters.

6. If you are making a one-off circuit you don't need to do all this, just get typical values, calculate function and operating envelope, and make a one off. Then check to see if it's near your calculations. But don't assume because you made one that works, you can make many and won't have problems.