Haven't "launchers" existed for decades at this point though? I remember Crunchbang (RIP) having something similar for example, and that must have been almost two decades ago at this point.
In this case, Walker is the launcher being used in Omarchy, https://github.com/abenz1267/walker. It's not specific to Omarchy.
One of Walker's features is being able to create your own custom menus quite easily with shell scripts.