Hey @AndrewH!
Just want to add a more complex version of the example given above to illustrate some of what might be possible in Retool. Again, there isn't a built-in way to generate a component that does exactly what you're looking for but, having done some experimenting, it seems there are certainly a few different approaches you might take. The following is just a start, but might give you some ideas as to what kind of customization is possible.
It uses a schema for each category that takes advantage looks something like the following:
{
label: "Characteristics",
dependencies: {
breed: ["."],
},
specifications: [
{
label: "Legs",
id: "legs",
selections: [
{
value: 2,
dependencies: {
animal_type: ["Bird"],
},
},
{
value: 4,
dependencies: {
animal_type: ["Cat"],
},
},
],
},
{
label: "Color",
id: "color",
selections: [
{
value: "Brown",
dependencies: {
animal_type: ["Cat"],
},
},
{
value: "Black",
dependencies: {
animal_type: ["Cat"],
},
},
],
},
],
},
Dependencies are arrays of strings to be matched on to check whether or not the user has selected the necessary values to enable either a category or particular option in a specification. The matching is done using some preloaded JavaScript:
window.checkDependencies = (dependencies, user_selections = {}) => {
for(let key in dependencies){
if(!dependencies[key].some(value => user_selections[key]?.match(value))){
return false;
}
}
return true;
}
Throughout, nested listview syntax is used to access different parts of the schema. The user selections themselves are stored in a temp state, so each select has a form data key pulled from the underlying schema:
and an event handler to store the data:
Then the visibility of certain options is done by checking the option's dependencies against the user selection:
Something similar is done for the labels/listviews that comprise each category:
Feel free to play around with it yourself using the attached JSON! Hopefully, it gives you some ideas to try that fit your specific case a bit better 
dynamic_listview_selects (3).json