Recently flew from Porto to Paris and was impressed with the boarding process. There were 4 signs, one for each zone (zone 1+2, 3, 4, 5), which led to 4 queues. Once zone 1+2 was done boarding, the queue from zone 3 was allowed to board etc. It helps that the airport has physical space to allow such a boarding process while maintaining 1,5m distance between passengers.