See this article which was written to clear up this confusion:
https://blog.wikichoon.com/2020/06/virt-manager-deprecated-in-rhel.html
From that article:
TL;DR: I’m the primary author of virt-manager. virt-manager is deprecated in RHEL8 in favor of cockpit, but ONLY in RHEL8 and future RHEL releases. The upstream project virt-manager is still maintained and is still relevant for other distros.