Flatpak

1

Install Flatpak.

sudo apt update
sudo apt install flatpak

Add Flathub so Ubuntu can fetch required runtimes if your bundle does not include them:

flatpak remote-add --if-not-exists flathub https://flathub.org/repo/flathub.flatpakrepo

Restart after this if Flatpak was not already installed:

sudo reboot

2

Install the local Flatpak.

For a .flatpak bundle:

flatpak install --user ./*.flatpak

If Ubuntu asks whether to install required runtimes, say yes.

To verify in the terminal run:

flatpak run io.github.xander_haj.Z3R

The Flatpak should be installed in your applications folder now.

3

Add the .dat file.

In Files, navigate to ~/.var, then app/io.github.xander_haj.Z3R/data/Z3R. Place zelda3_assets.dat there and modify the INI before launch.

4

Uninstall it before testing a newer build.

flatpak uninstall --user io.github.xander_haj.Z3R

Then reinstall the new bundle:

flatpak install --user ./*.flatpak

If you want a cleaner uninstall including unused runtimes:

flatpak uninstall --user --unused