I have 2 things that require I stay on the current version of my Fedora 32 kernel

1. NVidia proprietary driver that doesn't seem to auto install despite being dkms enabled
2. VMware® Workstation 15 Pro version 15.5.6 build-16341506 which won't run on kernels later than 5.6.19-300.fc32.x86_64

This is what you need to edit to stop dnf update from automatically making the latest kernel the default

Edit /etc/sysconfig/kernel

# UPDATEDEFAULT specifies if kernel-install should make
# new kernels the default

# change this from yes to no
UPDATEDEFAULT=no

# DEFAULTKERNEL specifies the default kernel package type
DEFAULTKERNEL=kernel-core