Depends on what you mean with stable, at least they are more recent than 0.23.
0.23 was followed by 1.0.
r = Android 11, q = Android 10
The letters come from Google’s internal references before the release of new Android versions, see https://en.wikipedia.org/wiki/Android_version_history.
/e/OS versions can be based on different underlying Android versions, depending on what is available to work with on a device.
If Settings - About phone - Android version gives you Android 9, then see here … Fairphone 3/3+ (FP3): OTA upgrade from Android 9 (Pie) status
No, as the filename says, it is the dev version, see here … https://doc.e.foundation/build-status
If you want to know what you are running now accordingly, see Settings - About phone - Android version (tap on it) - /e/OS version.
stable builds would be here … https://images.ecloud.global/stable/FP3/