I live in a tiny micro studio apartment by myself - I could definitely work from home there but I’d quickly turn into an un-socialized hermit doing that long term. For better or worse I find there’s some value actually getting myself out of the house and interacting with people IRL even if it’s just work stuff.
Eating fish (vitamin D) regularly and making more of an effort to get outside during daylight hours seems to work for me. Vitamins/supplements are okay but aren’t a replacement for real nutritional sources.
Before that I used to eat less fish and mostly managed to get outside after daylight hours - definitely had the same sort of low mood / being sluggish and unmotivated as you describe.
I don’t have any good suggestions for you but I do agree, Nextdoor is trash. I removed it from my phone and usually avoid logging into the site at all. They seem to be in a competition with Facebook to figure out which of the two is the bigger dumpster fire.
re: marketplace, for now I just go back to Craigslist if I want to scan for anything interesting someone is selling, or giving away for free.