Kernel update insists on trying to create symlinks on /boot even though /boot is vfat

This is a recent kernel update on Ubuntu Mate 20.04 running on Raspberry Pi.

apt-get -y update first produced:

Setting up linux-image-5.4.0-1042-raspi (5.4.0-1042.46) ...

Failed to create symlink to vmlinuz-5.4.0-1042-raspi: Operation not permitted at /usr/bin/linux-update-symlinks line 64.

dpkg: error processing package linux-image-5.4.0-1042-raspi (--configure): installed linux-image-5.4.0-1042-raspi package post-installation script subprocess returned error exit status 1

dpkg: dependency problems prevent configuration of linux-image-raspi:

linux-image-raspi depends on linux-image-5.4.0-1042-raspi; however: Package linux-image-5.4.0-1042-raspi is not configured yet.

dpkg: error processing package linux-image-raspi (--configure): dependency problems - leaving unconfigured Setting up kpartx (0.8.3-1ubuntu2) ...

dpkg: dependency problems prevent configuration of linux-raspi: linux-raspi depends on linux-image-raspi (= 5.4.0.1042.77); however: Package linux-image-raspi is not configured yet.

dpkg: error processing package linux-raspi (--configure):

dependency problems - leaving unconfigured Processing triggers for man-db (2.9.1-1) ...

Errors were encountered while processing: linux-image-5.4.0-1042-raspi linux-image-raspi linux-raspi

E: Sub-process /usr/bin/dpkg returned an error code (1)

then /etc/kernel-img.conf was changed to: do_symlinks = no

no_symlinks = yes

do_bootloader = no

link_in_boot = no

Now, apt -y update produces:

After this operation, 0 B of additional disk space will be used.

Setting up linux-image-5.4.0-1042-raspi (5.4.0-1042.46) ...

/etc/kernel-img.conf: W: ignoring no_symlinks; only symlinks are supported

Processing triggers for linux-image-5.4.0-1042-raspi (5.4.0-1042.46) ...

/etc/kernel/postinst.d/initramfs-tools: update-initramfs: Generating /boot/initrd.img-5.4.0-1042-raspi

Using DTB: bcm2711-rpi-4-b.dtb

Installing /lib/firmware/5.4.0-1042-raspi/device-tree/broadcom/bcm2711-rpi-4-b.dtb into /boot/dtbs/5.4.0-1042-raspi/./bcm2711-rpi-4-b.dtb

Taking backup of bcm2711-rpi-4-b.dtb.

Installing new bcm2711-rpi-4-b.dtb.

ln: failed to create symbolic link '/boot/dtb-5.4.0-1042-raspi': Operation not permitted

run-parts: /etc/initramfs/post-update.d//flash-kernel exited with return code 1

run-parts: /etc/kernel/postinst.d/initramfs-tools exited with return code 1

dpkg: error processing package linux-image-5.4.0-1042-raspi (--configure):

installed linux-image-5.4.0-1042-raspi package post-installation script subprocess returned error exit status 1

Errors were encountered while processing: linux-image-5.4.0-1042-raspi

E: Sub-process /usr/bin/dpkg returned an error code (1)

Obviously, the problem is that the system is trying to make symlinks on vfat, which doesn't support them.

Any idea how to make it stop? or how to get apt to back out & forget the bad update?