Hi kazgor
As this interested me as well, I did a quick search and it seems that they are going to switch to v3 after it becomes stable.
There’s a guide to manually install, but no idea about it: https://sonarr.tv/#downloads-v3-linux-debian
Link here: https://dietpi.com/forum/t/sonarr-v3/3856/1
Cheers and happy new year 