When you try to install using package manager on CentOS Linux after EOL date (December 31, 2021) you'll get an error:
Error: Failed to download metadata for repo 'appstream': Cannot prepare internal mirrorlist: No URLs in mirrorlist
That's because repositories have been moved to centos project vault location. A way to handle is to point urls from repos configuration to centos vault location. Then it's possible to update CentOS (for example, from previous version 8.4.2105) to the latest version 8.5.2111. From there you could shift towards Rocky Linux or CentOS Stream following recommended procedure.