I'm really confused why people are so upset about them being taken off of app stores.
It's possible to download an app outside of the app store and install it, even on iPhone. It's not even hard. On Android, you download the apk file and push install. On Apple, the developer provides you with a development build that you download, install and need to manually approve on the device.
Binance did this for years because Apple didn't allow them to have their app on the app store since they weren't a business approved to operate in the US.
I wanted to use it, so I got it from their website, downloaded it, and used it for years.
Also, Parler is a web app. You can use it with feature parity on any device at any time from any browser.
It feels like that point is being massively overblown, to me.
And Amazon is still a private business, and there are several hosting alternatives like Digital Ocean that offer just about the same features (load balancing, bastion hosts, etc.) who will gladly take Parler's money.
It feels like we are overreacting to something that the free market will sort out (assuming we let it operate as a somewhat quasi-free market....but who the hell knows on that point anymore)
EDIT: It looks like Apple started restricting how you can install apps that are not on the app store, and it's much more restrictive now, so they do have a stranglehold on that (though you can make a web app with full feature parity pretty easily, and people who believe strongly enough in Parler's mission would sell their iPhones to get an Android if it was that big of a deal to them)