Yes, it is generally compatible with Joomla 4.x.

However, this is not recommended for long-term use, as Joomla 4 is now an older branch and many extensions moving forward are primarily optimized for newer Joomla versions. For better stability, security, and full feature support, it is advisable to upgrade your Joomla installation to a more recent version.

Daniel, please read the SPPB documentation. The explanation is there.

In general, Joomla 4 is not supported anymore, also by Joomla Development team. You are using it at your own risk. SPPB 6 may work on J4, but we didn't test it.