So it works (and probably worked 
Interestingly enough the method with ‘Shift then mouse’ doesn’t works for me 
but I tried while quite tired after too much of a night’n’day I’ll try harder later 
@Loki_Harfagr I edited my question, realizing too late that I was too vague. From the beginning, I wanted to mouse-drag and lock axis, and I never wrote that anywhere! My mistake, I am sorry to have caused a misunderstanding and make you lose your time.