On Buster you need to also apply these commands to permanently disable swap:

sudo dphys-swapfile swapoff
sudo dphys-swapfile uninstall
sudo update-rc.d dphys-swapfile remove
sudo rm -f /etc/init.d/dphys-swapfile

sudo service dphys-swapfile stop
sudo systemctl disable dphys-swapfile.service