Regarding realtime kernels, canonical charges money for their rt preempt kernels, so if you want to avoid that, you would have to compile your own realtime kernels too, which might be a daunting task, depending on your hardware.
Building the kernel is not hards, it just takes some time. This snippet builds a debian .deb file which should be installable on Ubuntu (but there are other commands that install the kernel for you directly/
Code:
apt update
sudo apt install -y build-essential bin86 libncurses5-dev pkg-config libssl-dev dwarves bison flex gnupg libelf-dev libssl-dev wget qtbase5-dev debhelper rsync git
mkdir rtlinux
cd rtlinux
git clone -b v6.3 --depth 1 https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git linux-6.3
wget https://mirrors.edge.kernel.org/pub/linux/kernel/projects/rt/6.3/patch-6.3-rt11.patch.gz
tar xvf linux-6.3.tar.xz
gunzip patch-6.3-rt11.patch.gz
cp patch-6.3-rt11.patch linux-6.3
cd linux-6.3
cat patch-6.3-rt11.patch | patch -p1
git add *
make xconfig
#Set the following: General Settings/Preemption model = Fully Preemptible Kernel
#Save then exit (Click on General settings and select option on the right side.
# These keys override security and key settings to allow .debs to be built
scripts/config --disable SYSTEM_REVOCATION_KEYS
scripts/config --disable DEBUG_INFO
scripts/config --enable DEBUG_INFO_NONE
scripts/config --set-str SYSTEM_TRUSTED_KEYS ""
make -j4 deb-pkg LOCALVERSION=-linuxcnc
Today I would go for the 6.5 kernel (or 6.6) but it would need a bit of work to revise the script.
This is code from kernel.org so its distro independent
