Have you shared your SP List data source (which used in your shared app) to the guest?
Firstly, if you want the guest user to access data from your SP List within this shared app, you must share your SP List to the guest. More details about sharing app resource in PowerApps, please check the following article:
In addition, when the guest user run your shared app, it would ask them to provide their own credentials to create a connection to these data source (SharePoint connector & Office 365 Users connector) used in this app, it would not still use your credential to create connection.
So you could not shared your Office 365 Users connection to the guest, these guests would use their own credentials to create connection to Office 365 Users connector rather than yours.
If you want these Guest to use your credential to create connection to SharePoint List and office365 Users, I afraid that there is no way to achieve your needs in PowerApps currently (unless you tell them your credential, e.g. UserName, Password, ...).
More details about sharing app in PowerApps, please check the following article: