The free version of the addon from February 2024 can be found for download on archive.org:

Download: web.archive.org/web/20240524062951/https://addons.mozilla.org/firefox/downloads/file/4233940/autofill_quantum-11.9.0.xpi

Mirror: files.catbox.moe/jtf3c4.xpi


(Make sure to turn off auto-updates for the addon)

---
Freemium should be done by adding additional features and charging for those (if it is done at all), not by restricting already present features.

Also take note that the developer went out of their way to remove downloads for historical versions of the plugin from the extension's page. Versions that would have performed these functions for free.