Trying to upgrade Kali on my Raspberry Pi (based on the 32-bit Offensive Security RPi 2020.2 build), kali-themes 2020.3.0 fails to install:

sudo apt upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
3 not fully installed or removed.
After this operation, 0 B of additional disk space will be used.
Do you want to continue? [Y/n]
Setting up kali-themes (2020.3.0) ...
cp: cannot create symbolic link '/boot/grub/themes/kali/background.png': Operation not permitted
dpkg: error processing package kali-themes (--configure):
installed kali-themes package post-installation script subprocess returned error exit status 1
dpkg: dependency problems prevent configuration of kali-desktop-core:
kali-desktop-core depends on kali-themes; however:
Package kali-themes is not configured yet.

dpkg: error processing package kali-desktop-core (--configure):
dependency problems - leaving unconfigured
dpkg: dependency problems prevent configuration of kali-desktop-xfce:
kali-desktop-xfce depends on kali-desktop-core; however:
Package kali-desktop-core is not configured yet.

dpkg: error processing package kali-desktop-xfce (--configure):
dependency problems - leaving unconfigured
Errors were encountered while processing:
kali-themes
kali-desktop-core
kali-desktop-xfce
E: Sub-process /usr/bin/dpkg returned an error code (1)

This appears to be because the /boot filesystem is vfat.