Is Firebase now mandatory for use of Google Analytics Mobile Properties?

Re-iterating the steps here from the same document for information to be available in same post:

1. Sign in to your Google Analytics account.
2. Click Admin.
3. In the PROPERTY column, select Create new property from the dropdown menu.
4. Select Website.
5. Provide a Website Name. You may use the name of your app.
6. Provide a Website URL. You may use your company URL or the URL for your app’s marketing site.
7. Click Get Tracking ID.
8. In the VIEW column, select Create new view from the dropdown menu.
9. Select Mobile app.
10. Provide a Reporting View Name.
11. Click Create View

Google have published instructions on how to set up a new mobile property using the Google Analytics Services SDK.

You can find them in Google Support, Analytics Help as Analytics for mobile apps.