Joomla 4 isn't anticipated to be fully released until late this year (I've heard Sept-Nov, but it's still too far out to have a definite timeline). Before then, Joomla 3.9 will be available which will have a compatibility layer so that an extension can work for both Joomla 3.9 and 4.0 at the same time. We fully plan to support Joomla 4 when it's available and have begun some testing with the alpha build. We do not anticipate a release of JFBConnect specifically for Joomla 4 for at least a few more months.
I hope that helps answer your question, but should you need anything else or have any other input, please let us know.
Thanks,
Alex