This is just a bit of transparency on our development environment.
Currently Joomla 3 is still our development environment. This means we're primarily concerned with maintaining Joomla 3 backwards compatibility. This however will be changing soon. After release of CB Activity 6.0.0 stable is done (still got awhile!) I will be switching my development environment to Joomla 4. This would then mean our focus is being as compatible as possible with Joomla 4. Joomla 3 will then receive fixes as needed, but all future UX and design will be taking into account the Joomla 4 default template and not Joomla 3 default template so it's possible there will be styling issues in the future.
The roadmap for Joomla 3 compatibility is roughly the same as Joomlas own EOL (end-of-life), which is currently August 17, 2023. Our new API library CB Framework will begin development early next year (not so far away now!) after CB Activity 6.0.0 and some other high priority tasks. CB Framework will only support Joomla 4. However the plan is to support Joomla 3 until Joomla 3 EOL in a plugins last major release. So for example CB Activity 6.0.0 is Joomla 3 compatible, but CB Activity 7.0.0 will not be and will be using CB Framework BUT CB Activity 6.0.0 will still receive bug fixes (no new features!) until Joomla 3 EOL. This will afford everyone plenty of time to prepare their sties for Joomla 4 migration or ensure sites that want to remain on Joomla 3 will have plenty of fixes until EOL.
Note this is all personal choices for my development cycle and not all products are subject to this. I just wanted everyone to know that we are absolutely continuing to push forward and will be here for years to come!