Leave the rest of us poor folk alone so we don’t have to seek expensive legal counsel.
So if you offer infrastructure, you cannot offer managed DBs there, if you have a market place you cannot sell on it, if you have an app store, you cannot sell apps there. Etc etc
I don't know anything about the legal side of things, but although I can see the appeal of a short blacklist, I think it would be a can of worms.
Still, you'd probably need a license steward to keep the list of companies up to date, and you'd keep the list in an annex. Alternatively you'd need to pick some objective thresholds, such as "more than 1 T$ market cap or more than 100 G$ global annual revenues". This is the approach the EU followed with the Digital Markets Act.
(I'm not saying that I'm endorsing such an approach.)