Realtime Kernel

The CentOS 8 Stream distribution has a Real Time kernel available.
To enable it, first run the pbase-preconfig-realtime-kernel package which simply enables the CentOS Stream-RT yum repository. Then run the pbase-realtime-kernel package to install the realtime-kernel and related utilities like tuna.

yum -y install http://pbase-foundation.com/pbase-repo.rpm
yum -y install pbase-preconfig-realtime-kernel
yum -y install pbase-realtime-kernel

Finally, reboot to activate the new kernel.

After the kernel is installed it will still require tuning as documented in the Red Hat guide:
RT-Kernel Post-Installation Instructions