To use Extended Remington Layout for linux you need IBus in your sistem

Install IBus

install these packages
ibus ibus-m17n m17n-db if you are using ubuntu run this in terminal
sudo apt install ibus ibus-m17n m17n-db
for more detailed info refer swanalekha documentation

Setting Up IBus

Most GNOME systems are well-integrated with IBus by default.

If you’re not using GNOME, you will need to setup IBus. ArchLinux Wiki has good information on setting up IBus: https://wiki.archlinux.org/title/IBus

IBus setup might be a bit tricky in KDE. It can be easily setup in ArchLinux by installing ibus-input-support.

Install poorna

clone the repositoty
copy ml-poornaremington.mim to /usr/share/m17n\

it can be done through following commands in terminal

git clone https://gitlab.com/smc/poorna/poorna-remington-linux.git
cd poorna-remington-liux
sudo cp ml-poornaremington.mim /usr/share/m17n

then add the layout to your Ibus preferences.
in ubuntu you can add keyboard from settings->keyboard

Remember this

to work 4 layers in poorna you have to select Right Alt from alternate charecter key option