While I see what you mean, these two phenomena are really two sides of the same coin. If I'd wager a guess, I'd say OP is probably referring to cases such as [0]. Regardless of which mechanism is at play though, the end result is the same, either rising prices through collusion or rising prices through lowered supply. Both also benefit anyone else doing it the other way, so it results in highly lopsided markets.

[0] https://www.axios.com/2023/11/02/dc-housing-rent-antitrust-l...