If you care about CentOS (and you should), then you should read this (please note, I did not choose the titles of the following articles or their URLs, but it does seem like that move from IBM's RedHad has some CentOS community members displeased). One key takeaway is CentOS 7 will have longer support then CentOS 8:
Well, we'll see what Claris will use for Linux in the next years.
For now they are still using CentOS 7, which is supported till 2024.
Lol, I saw that today. Practically upgrading 3 servers to CentOS 8 today, now it will be discontinued 2021...
This is a joke.
in German
Danke! 
Here's another article not listed above-
CentOS Linux is dead—and Red Hat says Stream is “not a replacement”
best
Kevin
RHEL seems to be over the top in terms of complexity and cost for the average SME with some 5 to 10-user FM license.
If Cloud is not an option, this is Mac Mini's sweet spot and the reason why we are not done with MacOS for FMS.
CentOS is not the only stable linux system by a long way 
as Christian @MonkeybreadSoftware points out FM Server runs on CentOS 7 which is supported until 2024. I am very hopeful that having released FM Server for a Linux platform the Claris developers will be able to find an alternative Linux distribution when the time comes. They will need to do so for FMCloud in any case presumably. I am going to continue moving my FM servers to CentOS Linux. There is even a good case to install CentOS as the OS on Mac minis!
Gregory Kurtzer the founder of Cent OS is currently building up a community around the open source successor called Rocky Linux: https://rockylinux.org/ . They put all efforts in a seamless transition of the project.
I also heard about a separate initiative: AlmaLinux.
I am not well versed to do any comparisons, but wanted to put it out there. It seems there will be many options to consider. I'm sure we are all curious to see what will be the guidelines from Claris about this, but it seems they have some time ahead of them to reach a decision.