Assuming you put down 20k on the 100k homes, you've returned 500%. That is incredible, but also fairly common story from the past few years. "I made it rich with real estate!" "How?" "Easy, buy at a historically low price."
The word is out, it's not a secret to success anymore. There is a pile of money out there waiting to invest in under-priced homes. This drives prices up! Because of this, a recession will not trigger a home price drop.
Property values will likely remain stable/inflated until something happens to break whatever math it is that keeps investors invested. It's the massive stockpile of homes investors gobbled up in 2009-12 that need to be released back to the market. It is a self-perpetuating cycle, people rent a home because home prices are too high due to investor held inventory. Then investors keep renting their asset out because renters don't graduate to buying.
I could be way off, or have missed something obvious, but I don't think real-estate is going to be the big moneymaker form this recession unless something happens to dramatically increase inventory in places with jobs.
An alternative mentioned in sibling comments -- which I completely agree with -- is to wait it out holding cash. This assumes you trust there won't be inflationary pressures. Depending on viewpoint there should be lots of that or deflation. It also assumes you're able to trust some institution to hold your cash and making it available when you need it. IMO that is less of a given, considering current private debt levels, if shit really hits the fan hard. But you never know, perhaps we can survive yet another 2008 type of crisis, and kick the can further down the road yet again.
Unless you have a PhD in quantitative finance, it's usually best to take it as axiomatic that you don't have a knowledge-based edge in the stock market, or anything similar.
But seriously though, the "Great Recession" was the largest downturn since the Great Depression. Do you expect the next one will be as bad or worse?
I'm not actively seeking to make money off a downturn aside from contributing to my 401k, which invests in a diversified mutual fund (I can't invest more actively for regulatory reasons). My main goal if that happens is to keep my job.