Hope this will turn into stupid question, but where is the manual.

Check the extras tab in GOG Galaxy or look for a downloads folder in your Steam directory. You should see the Guidebook in there.

beside soundtrack,avatars, etc there is only sourcebook for CP 2020, no guide/manual book for CP2077 (checked on gog and galaxy).

CP2020_Guidebook? Quick glance at that was for the PNP version of Cyberpunk.
I downloaded from the offline installers, not galaxy and not steam.

Technically, the Guidebook for Cyberpunk *is* the manual XD This game is based on the 1988 pen-and-paper game so that's your best bet really. Idk what you mean by a manual though. Like those hard copy booklets we used to get that had all the key bindings and mechanics descriptions in them?

No guide or manual. That's screwy.