I recall choosing to edit refind_linux.conf once a long time ago (to bypass Grub, and specifically use kernel 6.1, I think). I did edit it manually, but usually if you use the refind-install script, that’s set automatically.
This is the /boot/refind_linux.conf from a VM I installed rEFInd on last week. In this case it used kernel 6.6 which was installed by default; I removed the UUIDs for brevity:
"Boot with standard options" "root=UUID=xxxx... rw quiet splash resume=UUID=xxxx... udev.log_priority=3"
"Boot to single-user mode" "root=UUID=xxxx... rw quiet splash resume=UUID=xxxx... udev.log_priority=3"
"Boot with minimal options" "ro root=/dev/nvme0n1p2"