Does a football referee have a duty to prevent a team from using more substitutions than they're allowed to?

AS Roma lost a game against Spezia in the 2020-21 Coppa Italia because they exceeded the number of substitutions they were allowed to do, mistakenly thinking they could go for a sixth one in extra time.

If the referee had noticed what was about to happen, would he have been required to step in and stop the substitution (The referee: […] enforces the Laws of the Game, Law 5)? Or should he have allowed the substitution to take place, only to caution the players involved immediately after (For any other offences: […] the players are cautioned, Law 3)?

I’m asking because it seems to be "common knowledge" here in Italy that the referee shouldn’t actually do anything in a situation like this, essentially allowing the team to be punished by the league after the match has ended, though I have found no evidence supporting this course of action in the IFAB Laws of the Game.