More and more people come to see the Colosseum! After the 2018 all time record (7.650.519 visitors) in 2019 there was a little decrease. In 2020 there was the COVID closure but in 2021 museum were reopened.
The following table is from the official statistics of the Italian government.

Actually, another very visited Roman monument (more than 6 million visitors) has been the Pantheon. It was free, but since 2023 there is a 5 Euro ticket. Info here