$ cat /etc/sysconfig/kernel
# UPDATEDEFAULT specifies if kernel-install should make
# new kernels the default
UPDATEDEFAULT=yes <========
# DEFAULTKERNEL specifies the default kernel package type
DEFAULTKERNEL=kernel-core
Also, just to add to this conversation a bit. I run systemd-boot, not grub, for the bootloader. If your btrfs subvolume that is mounted as /boot is actually comprised of more than one physical device partitions, you will run into updating problems at one point or another since the mounted subvolume is not one contiguous block. In that scenario, which I find myself, the kernel updates do not get reflected in the bootloader entries. Systemd-boot silently fails during a (automatic) kernel update and unless you manually perform the update of (boot menu) entries in a terminal, you don’t see the error.
It could be. I did not mess with the default Fedora installation; however, I installed Btrfs Assistant after the installation to test the root snapshot and restore.
$ sudo btrfs subvolume list /
ID 256 gen 10194 top level 5 path home
ID 258 gen 10095 top level 269 path var/lib/machines
ID 259 gen 10020 top level 269 path var/swap
ID 269 gen 10194 top level 5 path root
ID 270 gen 10160 top level 269 path .snapshots
ID 271 gen 9698 top level 270 path .snapshots/1/snapshot
ID 272 gen 9716 top level 270 path .snapshots/2/snapshot
ID 273 gen 9845 top level 270 path .snapshots/3/snapshot
ID 274 gen 10010 top level 270 path .snapshots/4/snapshot
ID 275 gen 10115 top level 270 path .snapshots/5/snapshot
ID 276 gen 10145 top level 270 path .snapshots/6/snapshot
ID 277 gen 10160 top level 270 path .snapshots/7/snapshot
$ sudo lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINTS
zram0 252:0 0 8G 0 disk [SWAP]
nvme0n1 259:0 0 931.5G 0 disk
├─nvme0n1p1 259:1 0 600M 0 part /boot/efi
├─nvme0n1p2 259:2 0 1G 0 part /boot
└─nvme0n1p3 259:3 0 929.9G 0 part
└─luks-1fa7c339-8b6e-4cfc-b0d6-9dec5e846012
253:0 0 929.9G 0 crypt /home