Trying to re-enable SPI via the instructions toward the end of this thread:
https://discourse.coreelec.org/t/spidev-coreelec-9-2-2/11178/9
mount -o remount,rw /flash
fdtput -t s /flash/dtb.img /soc/cbus@ffd00000/spi@13000/spidev@0 status "okay"
fdtput -t s /flash/dtb.img /soc/cbus@ffd00000/spi@13000 status "okay"
echo "spidev" >> /storage/.config/modules-load.d/spi.conf
echo "spi-meson-spicc" >> /storage/.config/modules-load.d/spi.conf
reboot
UPDATE: The above worked nicely. I already had the spi.conf file, as I tried that first; I was missing enabling the relevant entries in the Device Tree.