Take Inter as an example in Serie A
Recently crowned Serie A champions Inter provide a good example of the upcoming rule change.
In the 2022-23 season, the Nerazzurri sold Cameroonian goalkeeper Andre Onana to Manchester United. In turn, they were then able to register two new non-EU players, as they had cleared up a spot in their squad. Thus, they brought in Chilean Alexis Sanchez that summer, and then Canada international Tajon Buchanan in January.
Theoretically, if Inter had kept hold of Onana, and assuming they didn’t sell any other non-EU player, they would not have been able to register Buchanan, as there would not have been any available slots.
Importantly, non-EU players who were already based in Italy do not count as a newly registered non-EU player. Alexis Sanchez does, as he was based in France, playing for Marseille, prior to his Inter return.