Help me fix a loose pedal-arm on a fixie! Basically, after a few months of riding my bike, the pedal arms start to loosen up every few weeks after skidding/backpedaling. I ended up having to pedal with one foot for at least 2kms today (I know, bad idea).

What is a possible fix for this problem?
I definitely saw metal dust from abrasion. Also may have seen a bit of worn thread on the pedal-arm. Someone told me to replace the self-extracting bolt on the NDS. There’s more to see in the photos I’ve added.

I greatly appreciate all your contributions, this really helps me out.
What is a possible fix for this problem?

Loctite.  Blue.
I have an FSA-based SRM power meter where the self-extracting crank bolt simply will not stay properly torqued without using Loctite.  That's probably pretty similar to the problems you're having. And I'm not backpedaling or skidding with that bike...
I bought the SRM crankset used, so maybe it was ridden with a loose bolt and the crankarm/spindle interface was damaged/distorted prior to my purchasing it, similar to what happens with a square-taper crankset.
I replaced the self-extracting bolt, and that didn't help.
But using blue Loctite works for me.
If that doesn't work for you, you might have to replace your crankset.
I don't recommend red Loctite...