I’ve had an Ubuntu crash and am not able to reinstall GnuCash on a trial version of Ubuntu 20.4.5. I seem to have installed 1.14.4-1~flatpak1~20.04.1 I don’t want to reinstall Ubuntu as I fear losing all the data on my HDD. From a terminal when I type sudo apt install gnucash it can’t find the package. I’m a complete neophyte with linux and find it impossible to find step by step instructions on how to do this without any knowledge of the complex linux environment.
Not sure how your flatpak is setup and if you have the remote enabled, but you should be able to use the instructions on the arrow down install button GnuCash | Flathub
flatpak install flathub org.gnucash.GnuCash
flatpak run org.gnucash.GnuCash