Install

Gridline targets Ubuntu 26.04 LTS (resolute) on x86_64 with GDM. The packages are not yet published to a PPA or the Ubuntu archive; until then, build the source package on the target machine.

sudo apt install build-essential debhelper
dpkg-buildpackage -us -uc -b
sudo dpkg -i ../gridline-session_*.deb

Dependencies (Hyprland, its portal backend, wayland-utils) resolve from the Ubuntu universe component automatically.

After install

Log out. Gridline appears as a session option at the login screen, next to Ubuntu and a bare Hyprland entry. Pick Gridline. Your previous session choice stays one click away.

Remove

sudo apt remove --purge gridline-session

GNOME was never touched. What the packages installed is what removing them takes away.