I don’t think a firm end-date for support has been given. The migration FAQ says:
For how long can I use 1.8?
Roon will provide ongoing support for 1.8 installation for some time after the release of 2.0, depending on the Roon 2.0 adoption rates. However, if you are more comfortable using Roon 1.8, you can always continue to run it on your own after the official support period ends.
Edit: and now I see that @mike has stated that support will continue “at least” until the end of December 2022.