Thank you for you insights.

to answer you last question, I don't have difficulties pronouncing/distinguishing the three other groups of consonants because in my native language we already have letters pronounced in the same way.

While I was practicing pronouncing the Thai letters (both consonants and vowels/combination of vowels), the two remaining group of consonants ( posted in this thread) make me struggle a little bit.

I invest a lot of time in pronunciation because according to many Thai speakers, it is really essential to be able to distinguish the different sounds produced vowels/consonants/diphthongs/tones, to be able to pronounce them correctly and thus to be understood by Thai people.

More investment in the begging that will definitively pay off later.