I'll tackle this in the most straightforward manner in Affinity Designer with a workflow which goes from how one naturally draws such a hand to the desired end result, quite quickly.
It appears far longer written than it is in practise: to draw this hand, with screencaps for documenting the process took me less than a minute.
One: draw the cartooney hand, using the Vector Brush tool, with independent lines for each curve as one would normally draw or sketch. In my case using an old Wacom Intuous graphics tablet, pressure feeding stroke width.
Two: Group all these curves. Double click into that group, select only those curves which (partially) form the outline of the hand against space, excluding any lines which only delineate internal details.
Three: Copy-paste these outside the group, hide the group in the Layers Palette.
Four: By left-clicking on a curve with the Node Tool (white arrow) add anchor-nodes where those lines intersect.
Five: Then, with that node still selected, click on Break Curve in the tool-dependent area of the menubar (break, join etc only show up when you have a curve selected and are using the Node Tool) to break the curve at that node.
Six: Delete the extraneous curve portion (the interior curve of the base of the thumb in this case). Select both the contour curves (in my case the thumb and the wristline curves) and select Join Curves - note you don't need to select the specific nodes at which they connect, and in fact they don't have to perfectly touch - just have both curves selected and it'll work well.
You will then see your curves joined into one.
Continue this for all the curves in the exterior contour of the hand.
Seven: Remove the stroke from this curve, and fill and apply transparency as you prefer for the final effect, and in my case I closed the curve along the wrist to control the wrist bump in the fill - I didn't have to do this - Affinity Designer will happily fill unclosed curves.
Eight: Now unhide your original drawn curves of the entire hand, having assured that this group is higher in the draw order in the Layers Palette than the whole hand fill we just constructed, and you're good-to-go!
Hope this helps.