As soon as version 10 is released. And that will be pretty soon, very likely before the end of 2022, but in reality it just means that you have to contact Mendix. They will not let you drown.
At my client, we still have an extensive Mendix 7 landscape. We heard from Mendix that Mendix 7 will not be deprecated before 06-2023. Furthermore, we heard that extended support will be available for Mendix 7 after this time. I'd be best to contact your Customer Success Manager.