Quick question about google play console internal testing / production app

I want to know if I already have a public app in the play store, if I insert a new release and publish it in the internal test channel,

Can anyone who has my app see the contents of the internal test?

or can I only see them because my Google account email is part of the tester group?

I can't understand.

Until now, since I wasn't sure, I created 2 apps, 1 internal test and 1 public, so I'm sure that only I can test it.

Yes to everything you said. Only the internal tester group can see it until you publish it live.