Follow these instructions: https://alire.ada.dev/transition_from_gnat_community.html
Start by installing Alire: https://alire.ada.dev/
You can still download GNAT Studio community edition (the official Ada IDE) here: https://github.com/AdaCore/gnatstudio/releases
That said, The Ada & SPARK VS Code extension is also available and it is recommended over GNAT Studio. https://marketplace.visualstudio.com/items?itemName=AdaCore.ada
You need to install gnat and gpruild though apt. You can then proceed to build alire (refer to the official documentation).
Launch an Alire Powershell then run alr run
Uses Alire (built from source) and 'local' toolchain based system packages gnat and gprbuild.
