Article 21 does. I've already mentioned Eden Hazard, but Pedro was another example; when he was transferred to Chelsea, Barcelona paid San Isidro 320k Pounds out of Chelsea's transfer fee.
Note: this only works when the training club(s) is (are) in a different football association to the buying club. For example, if we sold Greenwood to, say, Man. City next season, and Man. City then sold him to Burnley when he's 30, we wouldn't be due any solidarity contribution. If, however, City sold Greenwood to, say, Juventus at the age of 30, we'd be due this solidarity compensation.