You can't install anything without an Apple account. Just tried installing altstore.io to repeat my previous unsuccessful attempt.
Only users based in Brazil, Japan, or the European Union are able to install apps through alternative app distribution. The country or region of your *Apple Account* must be set to one of those countries or regions, and you must physically be located there. [0]
UPDATE: Also tried to install onside.io. No luck. The same popup:
Cannot Install App: You are not eligible to install apps from "onside.io".
Only users based in Brazil, Japan, or the European Union are able to install apps through alternative app distribution. The country or region of your *Apple Account* must be set to one of those countries or regions, and you must physically be located there. [0]
UPDATE: Also tried to install onside.io. No luck. The same popup:
Cannot Install App: You are not eligible to install apps from "onside.io".
[0] https://support.apple.com/en-us/117767 https://support.apple.com/en-us/118110