https://wccftech.com/google-ends-support-for-original-quality-photos-backup-on-pixel-3-series/

One of my favorite apps from Google is its Photos app, allowing users to backup their photos for free. However, while this used to be the case, Google did offer Pixel users more time compared to other Android smartphone manufacturers. However, the company has finally seen fit to take away free original quality backup on the Pixel 3 on its Google Photos app. Scroll down to read more details on the subject.

If you have set Google Photos backup enabled at "Original Quality" on the Pixel 3, it is time to step down to High Quality. This is due to the fact that backup in Original Quality is no longer supported for Pixel 3 and Pixel 3 XL. However, if you want to buy more cloud storage, you are more than welcome to do so but if you want to backup for free, you might have to choose High Quality instead.