I wouldn't recommend searching for "chemical imbalance debunked" unless you intend to confirm an existing bias. The internet will show you whatever you want, and there are enough people who distrust medical professionals that any search for "debunking" will be a minefield of fringe theories and grifters. I'd recommend someone start generally, searching for information about clinical depression, and then build on that to look at root causes and how the medical understanding of those root causes has changed over time.

One of the first search results for me was a paper published in Nature. Other top results were from respected institutions like the NIH and Harvard University. Hardly grifters or crazies.

The caveat you cite applies to basically any and all internet (or even media) consumption, and is therefore a non-argument.