Overlay File System (read-only SD card) seems broken?

pmarks

Running Raspbian 11 on my Le Potato, I tried to write-protect the SD card using these instructions:
  https://learn.adafruit.com/read-only-raspberry-pi

Afterward, it's still writable:
    $ mount
    ...
    /dev/mmcblk1p2 on / type btrfs (rw, ...)

Here's a Raspberry Pi, for comparison:
    $ mount
    ...
    overlay on / type overlay (rw, ...)

What should I be doing instead?

pmarks

I bludgeoned this script until it worked:

git clone https://github.com/adafruit/Raspberry-Pi-Installer-Scripts.git
cd Raspberry-Pi-Installer-Scripts
sed '1,10s,^exit 0,#exit 0,' -i read-only-fs.sh
sed 's,/boot,/boot/efi,g'    -i read-only-fs.sh
sed 's,ext4,btrfs,g'         -i read-only-fs.sh
sudo ./read-only-fs.sh  # Answer ynnny