This utility is an app indicator (tray icon) to help you reboot into other OSes, or UEFI/BIOS, or the same OS.
Instead of picking the OS you want during reboot at the grub menu, you can just preselect it from the menu here.
Basically it's a wrapper around grub-reboot. I've only tested this on Ubuntu 20.04, 22.04, 24.04.

apt install:

sudo add-apt-repository ppa:mendhak/ppa
sudo apt update
sudo apt install grub-reboot-picker

The application will auto start the next time you log in to Ubuntu.
You can also launch it directly by searching for Grub Reboot Picker in Activities

Click on the application icon.
A menu with grub entries will appear.
Click one of the entries.
After a moment, Ubuntu will reboot.
The grub menu item you chose should be preselected.

Configuration file or Configuration screen:

• Top level or double level menu items
• Nicknames for menu items

StartupNotify = true might be causing 'wait' cursor to appear

Run a single instance of the application

You can run this application directly from this git repo.

First get the dependencies

sudo apt install python3-gi python3-gi-cairo gir1.2-gtk-3.0 gir1.2-appindicator3-0.1

Clone this repo, then run the python script.

cd src
sudo ./grub-reboot-picker.py

Sudo is required here because grub.cfg may not be readable (0600 permission)

Using setuptools with stdeb.
This produces a source package, and then creates a .deb package in the deb_dist directory.

First, some build dependencies:

sudo apt install python3-stdeb fakeroot python3-all dh-python lintian devscripts

Then to build:

# Set the version and suite (noble, jammy, etc)
nano version.sh
# Update the changelog, carefully
nano CHANGELOG.md
# Read the version
source version.sh
# Clean everything
rm -rf deb_dist dist *.tar.gz *.egg* build tmp
# Create the source and deb
python3 setup.py --command-packages=stdeb.command sdist_dsc --suite $suite bdist_deb
# Run a lint against this deb
lintian deb_dist/grub-reboot-picker_$version-1_all.deb
# Look at information about this deb
dpkg -I deb_dist/grub-reboot-picker_$version-1_all.deb

The setup.py is the starting point, which runs setuptools. Which uses stdeb to run commands to create the .deb.
The setup.cfg contains arguments to use for the package generation, both for setuputils as well as stdeb for things like Debian control file, changelog, etc.
The MANIFEST.in includes non-code files which are still needed.
I've modified setup.py a bit to generate Debian's changelog from the CHANGELOG.md, it's very sensitive to spacing.

After building, to upload to launchpad, you have to extract the sources, then GPG sign, then use dput to push up. Then wait for launchpad to build the code, which can take up to an hour.

cd tmp
# Extract the source into a subdirectory
dpkg-source -x ../deb_dist/grub-reboot-picker_$version-1.dsc
cd grub-reboot-picker-$version/
# Build a debian package and GPG sign it
debuild -S -sa
# Upload to launchpad
dput ppa:mendhak/ppa ../grub-reboot-picker_$version-1_source.changes

There's a lot happening in a .deb file. For my own benefit, here are the files it creates, and their purpose.

The com.mendhak.grubrebootpicker.desktop file goes in two places.

/etc/xdg/autostart/ - ensures that the app is launched when the user logs in
/usr/share/applications/ - ensures that the app can be found when searching through Activities.

The com.mendhak.grubrebootpicker.policy is a polkit policy file goes in /usr/share/polkit-1/actions/.
This in turn allows the application to run pkexec reboot without a password prompt.

As part of the build the .py extension is removed. During install, the executable, extensionless Python script is put in /usr/sbin so that it's on the user's $PATH.