From 2021, the aviation industry is expected to realize carbon -neutral growth (against 2019 and 2020 emission levels). It seem they need to take necessary measures such as offsetting.

"According to the Assembly Resolution, the average level of CO2 emissions from international aviation covered by the scheme between 2019 and 2020 represents the basis carbon neutraltral growth from 2020, against which emissions in future years are compared. In any year from 2021 when international aviation CO2 emissions covered by the scheme exceed the average baseline emissions of 2019 and 2020, this difference represents the sector's offsetting requirements for that year. "
https://www.icao.int/environmental-protection/p
ages/a39_corsia_faq2.aspx

"Our second EUROCONTROL Data Snapshot is dedicated to the decline of CO2 emissions from flights by 57% in 2020 and the considerable variation between States."
https://www.eurocontrol.int/publication/eurocontrol-data-snapshot-co2-emissions-flights-2020