Mouse+Keyboard Indicators Issue

[curlycrow]

I'm playing with mouse an keyboard, I don't have a gamepad. In the prologue during the 'be quiet' sequence and in the very beginning of the 1st chapter when I had to give a hand to the concussed guy I kept getting this symbol for whatever actions I had to perform.
https://steamcommunity.com/sharedfiles/filedetails/?id=3292122308
When in the prologue it was specifically stated that I have to press the "s" button, in the hand-giving QTE there was absolutely no indications on which button that is. I tried clicking LMB and RMB but they both were wrong. I made a new save, sit through all the cutscenes and then tried the "s" button but it was also wrong. Am I misunderstanding something? How am I supposed to play a QTE-heavy game when I don't know what buttons to press?

[Jimi]

It looks like 'press and hold left mouse button'.