CentOS is moving its focus away from CentOS Linux to CentOS Stream. CentOS has been widely in use among the developer community as it is a variant of RHEL (RedHat). There are still many deployments both commercial as well as development where multiple CentOS linux machines are used. Some of them still using CentOS 7 and some moved to CentOS 8.
CentOS 8 has reached its EOL on 31st December 2021 where as CentOS 7 has EOL until 2024. So it is encouraged to update your CentOS linux to CentOS Stream.
The difference between these two is that CentOS Linux is downstream based while CentOS Stream is upstream based. CentOS Linux is a rebuild of RHEL (Red Hat Enterprise Linux) as such is it a downstream from RHEL. For example, CentOS 8.2105 version means that it was built from the RHEL 8.3 version which was release in the year 21 and month 05 (may).
CentOS Stream on the other hand is a upstream which means it is the development branch of RHEL so CentOS Stream 8 is the upstream for the next minor version of RHEL 8 and CentOS Stream 9 is the upstream for the next minor version of RHEL 9 and so on.
Therefore for CentOS Linux updates, it takes quite a while to get new packages and updates where us in CentOS Stream, it only takes a few days to get the latest updates.