How can I change the OCI Runtime in Podman

You can find the runtime_path defaults in /usr/share/containers/libpod.conf and overwrite them in /etc/containers/libpod.conf (on EL8, check man podman to find correct place for Your setup).
As there is no daemon this is the conifguration used for all the libpod commands that need to know that.

Edit: as stated by @jnbdz the probably more important default location: in rootless mode $HOME/.config/containers/libpod.conf

Container engines will read containers.conf files in up to three locations in the following order:

1. /usr/share/containers/containers.conf
2. /etc/containers/containers.conf
3. $HOME/.config/containers/containers.conf (Rootless containers ONLY)

Items specified in the latter containers.conf, if they exist, override the previous containers.conf settings, or the default settings.

Found this written at top of the /usr/share/containers/containers.conf