This is both the Strength and Weakness of Rocky Linux, CentOS 8.4, Alma Linux 8.4 and those OS’s that are descendants of RHEL they are TRUE "Bug-for-Bug copies of RHEL 8.x and beyond.
As a small matter IF you want top install KDE 5 in Rocky Linux 8.4 it can be done, but it is a PITA . Indeed I was never able to successfully install either CentOS 8.4 or Rocky Linux 8.4. It would a particular point in the install process then the install would throw up some type of ERROR message and the Install would come to a screeching HALT!! While trying to solve the install process, I came across a thumb drive of CentOS 8.3. It installed with no problems – though I had to install it something like 5 times because of USER ERROR. Once I had installed CentOS 8.3, I simply ran “dnf update” which rolled the system over to CentOS 8.4 This brings us back to your question of installing KDE (5.xx – unfortunately ). I am a long time – 20+ year – user of KDE, but KDE 5.x does not sit well with me and was considering jumping over to Cinnamon – which you can likewise install on CentOS 8.4.
My way around the CentOS 8.4 => Rocky Linux 8.4 was to do ALL – or at least most of all – my configuration in CentOS 8.4 BEFORE I ran the migrate2rocky -r command. In short bake in most of my configurations in CentOS 8.4 before I then migrated the whole to Rocky Linux 8.4, since, like you, I was not certain of HOW I would install KDE 5.x (now actually 5.18).
While there is a certain appeal to having a Bug-for-Bug compatible OS with RHEL, there are some MAJOR drawbacks to this approach. I discovered one such bug this past weekend that has been around for a L-O-N-G time but still has not been fixed, and the BUG affects ONLY RHEL 8.x, and of course, CentOS 8.x, and NOW Rocky Linux 8.4. The BUG deals with VMWare Player 15.x,y and 16.x.y. Just when you think you can start building or loading a Virtual Machine it throws up a “Exit Code 1” Error message. I ended up with the exact same “Exit Code 1” error message starting VMWare Player 15.0.0 all the way up to the Current Version of VMWare Player 16.1.2. As I said this is a well known BUG, but it remains UNFIXED. WHY?? Not a clue. Now could Rocky Linux FIX the BUG, or even deviate from the Bug-for-Bug ethos of RHEL?? Sure it could!!
Going back to the VMWare Player BUG, it exists ONLY in RHEL 8.x (… and CentOS 8.x and now in Rocky Linux 8.4; the BUG “Does Not” affect CentOS 7.9 as I have VMWare Player 16.1.2 running just fine on the Workstation, nor does it affect openSUSE 15.3 Leap, another OS I am currently evaluating as a replacement for CentOS. This brings us back to the Central Question for the Rocky Linux Team: Should Rocky Linux be an EXACT Bug-for-Bug copy of RHEL, or should Rocky Linux be committed to the BASIC idea of a Bug-for-Bug copy of RHEL, but tweaking their copy of RHEL but making it “their own” ie FIXING long standing BUGS that Red Hat seems neither to care about, or refuses to FIX. This is the equivalent – in some ways – of passing on a virus or disease which you know about, but which you refuses to take steps to mitigate. I am sure Red Hat will point their figures at VMWare, and I am equally sure that VMWare will point their figures back at Red Hat. It is the user of VMWare’s Player that bears the brunt of this BUG – truthfully I don’t care whose fault it is, I just care that the Bug be fixed. That the BUG does NOT affect CentOS 7.9 or openSUSE 15.3 Leap, and seems to be specific to ONLY RHEL 8.x, this is where Rocky Linux could play a huge role. There is nothing that prevents Rocky Linux from tweaking the Red Hat Code and fixing long standing bugs.
As to Robb’s assertion that “rocky linux will be a server distro. Then pragmaticly thinking, why add a DE (any DE)?” I disagree. I run a WORKSTATION and rely on KDE – even Red Hat provides a DE – GNOME – in their distro, and up until recently Red Hat provided both GNOME and KDE. To quote Robb, should Rocky Linux become a “Server Only” distro, then I can pragmatically predict that Rocky Linux will have a very short lifespan. The truth of the matter is that most of the people that are currently using CentOS Linux are a mixture of people who are running it on 1-2 machines as their primary OS so as to avoid paying the “Microsoft Tax”, and running an inferior OS on top of that, all the way up to small businesses, servers, and Super Computers. User experience ranges from noobys all the way up RHCE and everything in between. I use a DE (KDE 5.0) about 50% of the time and the CLI about 50% of the time. Why?? Because I have Parkinson’s Disease and as a result my typing skills suck! Using a highly configured DE such a KDE 5.x makes more than a little sense. …But I also have on this Workstation GNOME, Cinnamon, LDX, Mate, Xfce, and a few others. Why?? As backups, as well as DE for “Guests”, who might have some sort of preference… Plus while a CLI might be available to them, they will have really limited privileges, though more likely than not they will go shrieking through the house that there is a CLI in addition to a bunch of “pretty icons”. If Rocky Linux is going to succeed, then it has to reach out to whole bunch of different users or all types, it can NOT become pigeon holed as a server only OS.