Based on a handful of recent reports, Google appears to be testing some Material tweaks to Gboard's settings pane. Changes include new outline-style icons and the usual blinding white background.

Gboard settings in version 8.18 (left), and 8.22 (right).

Not all of our devices on 8.22 see the updated visuals, and in my testing those that do only get the changes if you access the keyboard's settings via a specific route. When accessing Gboard's settings via the keyboard itself on most of my devices the visual tweaks are present, but they're missing when accessing via the Settings app (Settings -> System -> Languages & input -> Virtual keyboard -> Gboard). As with all the numerous Gboard tests happening, YMMV; at least one device I tested that had the updated Material Theme layout lost it mid-testing.

Non-matching (left), and matching (right) navigation bar, toggled in v8.22 for some. 

On that note, both myself and some of our tipsters are also seeing the flag for navigation bar matching being enabled on 8.22, but much like these Material Theme tweaks, that isn't a universal experience. Some are also seeing a handful of other flags toggled in this latest update. Frankly, it's nearly impossible to keep track of Gboard changes, so many are being tested at any given time.

The updated Material Theme layout could also be related to the Pixel theme strings spotted in a recent Gboard teardown.

Interested parties can download the latest 8.22 beta at APK Mirror, or opt in to the beta test to download it via the Play Store.

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Thanks: Rafael Freitas, Bogdan Manole, Tycho Regter, and everyone who sent this in