My Raspberry Pi 4 was originally loaded with Ubuntu 21.04, but after yesterday's release of 21.10, I upgraded using the do-release-upgrade command.
Among the other upgraded packages, there was a new Linux kernel: prior to the upgrade, the kernel version was 5.11.0-1019-raspi, while a new version 5.13.0-1008-raspi was installed in the course of the upgrade.
After the requested reboot at the end of the upgrade process, I found out that kernel version 5.11.0-1019-raspi was still in use. I have attempted to reinstall modules such as linux-image-5.13.0-1008-raspi, linux-image-raspi linux-modules-5.13.0-1008-raspi and linux-raspi, as well as removing the old kernel version. I have confirmed that /boot/vmlinuz and /boot/firmware/vmlinuz point to the same file, and it is the one for version 5.13.0-1008-raspi. Furthermore, after removing the old version, even vmlinuz.old points to the new version, so I have no idea where the system is fetching the old version from. Note that there have been quite a few reboots in the process, even a physical one by removing the power cable.
Regardless of everything done above, the system still boots to 5.11.0-1019-raspi. I suspect there's a missing installation step that updates some kind of onboard memory on the Raspberry Pi.
Note that, ever since installing Ubuntu 21.04 in this board a few months ago, I've seen apt upgrade install new kernel versions -- I am made aware of this due to the need to recompile a custom kernel module. Thus, the upgrade has worked automatically in the past. I'm not sure why it's not working this time.
My question is: what do I need to do make the Raspberry Pi boot the new version of the kernel?
EDIT: adding the information requested in the comments:
$ mount | grep boot
/dev/mmcblk0p1 on /boot/firmware type vfat (rw,relatime,fmask=0022,dmask=0022,codepage=437,iocharset=ascii,shortname=mixed,errors=remount-ro)
$ ls -R /boot
/boot:
System.map-5.11.0-1019-raspi config-5.11.0-1019-raspi config.txt dtb-5.13.0-1008-raspi firmware initrd.img initrd.img.old vmlinuz-5.13.0-1008-raspi
System.map-5.13.0-1008-raspi config-5.13.0-1008-raspi dtb dtbs grub initrd.img-5.13.0-1008-raspi vmlinuz vmlinuz.old
/boot/dtbs:
5.11.0-1007-raspi 5.11.0-1019-raspi 5.13.0-1008-raspi
/boot/dtbs/5.11.0-1007-raspi:
bcm2711-rpi-4-b.dtb.bak
/boot/dtbs/5.11.0-1019-raspi:
bcm2711-rpi-4-b.dtb.bak
/boot/dtbs/5.13.0-1008-raspi:
bcm2711-rpi-4-b.dtb bcm2711-rpi-4-b.dtb.bak
/boot/firmware:
README bcm2710-rpi-cm3.dtb bcm2711-rpi-cm4.dtb.bak bcm2837-rpi-cm3-io3.dtb config.txt fixup4db.dat fixup_db.dat.bak start.elf start4db.elf.bak start_x.elf uboot_rpi_arm64.bin.bak
bcm2710-rpi-2-b.dtb bcm2710-rpi-cm3.dtb.bak bcm2837-rpi-3-a-plus.dtb bcm2837-rpi-cm3-io3.dtb.bak fixup.dat fixup4db.dat.bak fixup_x.dat start.elf.bak start4x.elf start_x.elf.bak vmlinuz
bcm2710-rpi-2-b.dtb.bak bcm2711-rpi-4-b.dtb bcm2837-rpi-3-a-plus.dtb.bak boot.scr fixup.dat.bak fixup4x.dat fixup_x.dat.bak start4.elf start4x.elf.bak uboot_rpi_3.bin vmlinuz.bak
bcm2710-rpi-3-b-plus.dtb bcm2711-rpi-4-b.dtb.bak bcm2837-rpi-3-b-plus.dtb boot.scr.bak fixup4.dat fixup4x.dat.bak initrd.img start4.elf.bak start_cd.elf uboot_rpi_3.bin.bak
bcm2710-rpi-3-b-plus.dtb.bak bcm2711-rpi-400.dtb bcm2837-rpi-3-b-plus.dtb.bak bootcode.bin fixup4.dat.bak fixup_cd.dat initrd.img.bak start4cd.elf start_cd.elf.bak uboot_rpi_4.bin
bcm2710-rpi-3-b.dtb bcm2711-rpi-400.dtb.bak bcm2837-rpi-3-b.dtb bootcode.bin.bak fixup4cd.dat fixup_cd.dat.bak overlay_map.dtb start4cd.elf.bak start_db.elf uboot_rpi_4.bin.bak
bcm2710-rpi-3-b.dtb.bak bcm2711-rpi-cm4.dtb bcm2837-rpi-3-b.dtb.bak cmdline.txt fixup4cd.dat.bak fixup_db.dat overlays start4db.elf start_db.elf.bak uboot_rpi_arm64.bin
