Can I limit the acess by email in a Basic or Pro Version of the app or do I need to pay for the Private App Version and have 20 users - $2 per user.
At this moment my app it is only a Personal App, free of charges, and I am trying to know what plan works better, since I want to limit the app to certain users.
For the content limitation/restriction
Yes, of course you can
You can restrict content by categorizing the users (admin/editor/viewer, etc.) whatever you want, just provide the role for each user.
You can even create restriction for each component.
For free version you could choose âpublic with emailâ
In the Layout mode, choose Features tab, then set the filter for the content restrictions
âLimit the item displayed based on their propertiesâ, click Add Filter.
You will need to upgrade Pro version while you need:
For more information 
https://docs.glideapps.com/all/etc/faq/limits-on-free-apps
Abdullah
I havenât tried yet but if I limit those users based on their role, does anyone outside of my user database that have access to the link to access the app can view and edit the content of the app or only the people that I have pre authorized?
Anybody will be able to sign in, but with the right filtering and visibility settings, they wonât be able to visibly see anything in the app. However, the data is not secure and someone with enough technical knowledge will still be able to access the underlying data since it will still be downloaded to the device. A free alternative is to apply row owners to the data, but this only works if any of your users will not be sharing any data. Row owners only allows the data that the user owns to be downloaded to the device.