Ask HN: Finding a second part-time job for some extra cash?

I find it bizarre having to ask this question because by almost all standards I have a high income (let's say between ~$150-180k). I'm comfortable and not under any financial duress, but even at that income I'm saving very, very little living in a HCOL and high tax city.

I'm a senior level engineer and good at what I do. I'd love to find some part-time way to make some cash in the evenings and weekends that doesn't require a long 6+ month contract or w\e. Something where I can jump in, do the job, and jump out.

Upwork is close but I'm finding that many people posting there are looking for things like full mobile apps for $400 which is absurd.

Where can I find this sort of work?