Currently the lowest possible sound volume is too loud.
Too loud for music and especially for phone calls.
I am currently using an app to adjust that bevavoir,
but the volume buttons will overwrite that every time.

Is / will it be possible somehow to increase the steps of
the volume sliders to get better granularity
(maybe 30 or 45 instead of currently 15, which the hardware can handle)
or may there be another option like making the current setting half as loud 
(the opposite of the already available "BestLoudness" setting in the sound settings menu)?

Thanks

Hi there. Just press a volume button and then slide the volume level with your finger in the display

That does not seem to work, since the volume inbetween the steps is as loud as directly on one of the 15 steps (the next available step with sound difference).
It is also inconvienent to adjust the volume on the screen when there are buttons for it.

Impossible to go lower... There is in minimum and I can't go down

Perhaps you have "BesLoudness" on?
settings>sounds>advanced>sound enhancement>BesLoudness

(That's not a typo, I presume it's meant to be "BestLoudness" but someone didn't spell it correctly)

Can anybody else confirm such issue? Can you guys provide a video of it and a video of you adjusting volume by touching the slider?

I tried this morning WhatsApp videocall with Besloudness off..... Same thing... Too loud

I think the recent update fixed this, my volume levels are much better now.l

Great! problem solved