I have not found this to be true. In fact, if you do a video views ad for a live stream Facebook tends to increase your organic reach but this is mostly on live video because that is what they are pushing right now.
I have not experienced any decrease though after running an ad. I would however suggestion "boosting a post" as a common practice.
This is generally not the best use of your money and doesn't always line up with your objectives in running an ad .
You should definitely invest in a course, mine or someone else's, that will teach you how to run ads using the ads manager and how to interpret the results so you can optimize them to get the best bang for your buck.