That post is from Nov 2023, and at that time latest version of fr24feed was 1.0.44-0 . Since then there have been several new versions, the latest released yesterday is 1.0.46-2.
Please use following commands to install latest version:
wget http://repo-feed.flightradar24.com/rpi_binaries/fr24feed_1.0.46-2_armhf.deb
sudo dpkg -i fr24feed_1.0.46-2_armhf.deb
sudo fr24feed --signup