I recently went all the way with a Sacshe ignition, DynaTek coils and a Shendingen regulator (https://www.roadstercycle.com/
Before jumping to conclusions, give your wiring a really good inspection and make sure your grounds around the battery and regulator are all clean and conducting. Then move to your fuse box; again check everything and make sure all is clean and conducting. I have an old analog multi meter with a buzzer function for continuity checks. Love it; perfect for these jobs.
A very typical failure point is the insulation of the 2 yellow leads from the alternator at the regulator connectors end; I think the wires are too small in diameter and simply get too hot at the regulator plug end. When there's no insulation left, the exposed wires are not supported and can flex and break so check. I replaced the last 6 inches of wire with a slightly heavier gauge on my bike.
Next test the alternator output; disconnect the two yellow wires from the regulator and hook them up to a multimeter set on alternating current
and anything over 100V. Start the bike and see what you get; alternator stators typically either work or don't, so if you see nothing, then either one or both of the wires is broken or the stator itself has a broken wire or short. Check each yellow for continuity to ground; you should not see any; if you do there's probably a short in the alternator stator. Alternator stators can be repaired so don't rush into buying a new one.
If you do see an output from the alternator and your yellow wires were good then the regulator is the next likely culprit. I'm pretty sure that all Darmahs have 12V, 28A regulators to handle the electric starter. There are some simple tests you can perform to test a regulator; just Google it. You will need a multimeter with a a diode test function. If your regulator is toast then you have the choice of replacing it with the same or going my route with a more modern Mosfet style but be warned; the one I got, a FH020AA, is slightly bigger than the original. I was able to fit it on my MHR on the same frame plate with a few tweaks. I'm not sure where the regulator lives on a Darmah. If you do go this route, tell me and I'll send you my wiring updates for this mod.
I should have started with the battery; if your battery is tired then you will have charging problems, starting problems and a weak spark. Weak batteries are often blamed for wrecking sprag (starter) clutches too. Batteries do not live forever and have a finite lifetime even when babied. You could take your battery to a local auto shop for a test; a good idea to put this possible issue to bed.
Please post back as you proceed and good luck.
Your Motopiat voltmeter looks like it is actually working. It's supposed to give you a "Gen" warning when the bike is running but not charging