Okay, here's how I set up my Leica Q3 43. I am fine art photographer producing work mostly for gallery shows, though I also take vacation shots, so I created two Profiles: Art (for my creative work), and P&S (for point-and-shoot vacation shots). I shoot exclusively Raw, so features like White Balance, Scene Modes, etc. are irrelevant for my work.
Art Profile. For my creative work, I use AF Focus Mode Field with back-button focus (explained below). Field is a good compromise between Spot and Multi-Field: it allows me to target an area for focusing but is not quite as precise as Spot. I switch to manual focus at times and when I do I often use Focus Peaking. I use Multi-Field for exposure metering since I find it does a very good job of evaluating a scene and setting exposure, though I use Center-Weighted metering occasionally.
I find Auto ISO Settings to be very useful. I set 800 as my maximum ISO value. I've run tests and found little to no noise at or below 800, though I increase ISO manually to as high as 3200 when needed. Lightroom's Denoise feature does an exceptionally good job of eliminating noise even for images shot at ISO 3200, though at the cost of some smoothing of texture. And I set 1/60 as my shutter speed limit. I know the Q3 43 has image stabilization, but I found that images are not as sharp at speeds slower than 1/60.
P&S Profile. The only change I make in this Profile is setting Focus Mode to Multi-Field (I do not use back-button focusing in this mode).
There are four customizable buttons on the Leica Q3 43
FN Button 1: I set this to AF-L (Auto Focus Lock). I place the small white square on the subject and press the button which locks focus, so now I can compose the shot knowing that focus remains locked. This feature means that depressing the shutter release partway does not affect focusing.
FN Button 2: I set this to Focus Mode so I can switch easily between Field and Multi-Field focusing methods.
Thumbwheel Button. I set this to ISO, so I can override Auto ISO settings and opt for a higher ISO value, and I set the Thumbwheel itself to Exposure Compensation.
Center Button. I set this to Display Info so I can change the amount of information in the viewfinder.
Those are the main settings I use. I hope this helps, feel free to ask followup questions. Have fun, it's a great camera!