I comment a little on my problem, I have an app that I want to test on iOS, but before doing all the publishing in the store, I want to be able to show it.
Is it possible to load it in the Expo app and to keep it “saved” working even if the computer that sent it to it is turned off?
Yes, as mentioned here when you publish your app it is uploaded to CloudFront and Expo’s servers and then:
When publishing is complete, we’ll give you a URL to your app which you can send to anybody who has the Expo client.
and
As soon as the publish is complete, the new version of your code is available to all your existing users. They’ll download the updated version next time they open the app or refresh it […]
As explained here the Expo app downloads the published app from CloudFront and Expo’s servers. The development machine is no longer involved (until you want to publish a new version.)