I've worked out a technique for getting core files
back to "normal"
First I dnf erase everything with "abrt" in the name (or
at least everything I can erase which doesn't try to take
the whole system with it).
You'd think that would be enough, but no!
That leaves systemd stealing the core files now.
So the next step is to
echo "kernel.core_pattern = core" >> /etc/sysctl.conf
After a reboot core files are back to traditional
P.S. I know there is a /etc/sysctl.d/ directory,
but nothing I put in there ever seemed to make
core files work, so I fell back to /etc/sysctl.conf