I am aware that with Ionic you can create cross-platform applications. These can be created in Vue, React, Angular, etc. I do however wonder which dependencies are responsible for what.
In the background, as I can see in my package.json, the Ionic framework uses Capacitor. If you run the command ionic start myApp tabs with the Ionic CLI, then a new project is created and various dependencies are installed, including Capacitor.
However, I can just as easily add Capacitor to an existing Vue.js project and I also would be able to create a cross-platform application.
My guess is therefore that Ionic is simply an additional abstraction layer above Capacitor and has implemented some components that use Capacitor APIs and for example provides different styling on different platforms.
As @Everton-Costa said, Ionic came first than capacitor and always had a great effort on providing a multi-platform stack to build apps through html5/browser capabilities and cordova for native bridging. Ionic has started early with angularjs after that with Angular(N) and now its practically web framework agnostic. Ionic have great UI components that works nicely on many browser agents and performing good with different screen's sizes etc.
I see capacitor as cordova on steroids, its plugins/modules tries to be more platform independent (ios/android/web). for example, the storage plugin you don't have to handle stuffs like isAndroid()|| isIOS() or isDesktop() to perform storage operations, the module itself chooses the best strategies for the running environment.
"Appflow" is the paid product for easing with CI/CD.