Using a diode to protect a voltage regulator
First concerning the referred question, there are two protection diodes that do not meet your request, D3 to protect from applying negative voltage and D2 to protect the internal transistor at the output of the linear regulator.
Adding a diode in series is not a good solution, first because of the voltage drop that you've already mentioned and then because of the temperature effect and the fact that the regulator is not regulating the directly used voltage.
A FET has a lower voltage drop and a similar problem is resolved on Arduino boards using a FET but for a 5V supply by adding a voltage divider and a comparator as follows (Schematics Ref: https://electrosome.com/arduino-uno/):

If you want to apply a similar solution on the 3.3V you have to add also a voltage reference instead of the 3V3 applied to the comparator.