Why does the installer format matter?

Choose the package for the system people actually use. The documentation lists NSIS as an updater-compatible Windows target. For the documented macOS updater, the ZIP is needed to generate update metadata even if people download a DMG to install the first copy. Check the requirements for the exact version you use.

What needs to move with your release setup?

Keep the Electron code, packaging configuration and access to the signing and release services. Update files and their metadata must be available to the installed app. Check signing and update verification for your version, then confirm the app opens an existing saved file after updating.

Which files would you hand to a Mac tester?

Draw a first install and an update for a fictional Electron catalog app.

Separate the installer from update assets
Put the DMG in the first-install path. Label the ZIP and update metadata in the version 2 release path.
Add one saved record
Write where a fictional record is saved and mark the point where the installed app must still be able to read it.