The internet permission can be disabled in system settings, the option can be found in different locations.

For some devices:

• Long press the app icon on the screen
• App info or the ⓘ icon
• Mobile data & WiFi
• Disable options like Enable WiFi connection and Enable mobile connection

For Samsung:

• System settings
• Connections
• Data usage
• Manage app data
• Select SpamBlocker
• Change Network connection method to Off

If your phone doesn't have such options, you can also download the no-internet-permission-apk from the release page, which is built by the github action, it's a bit larger and non-reproducible though.