How can an Apple Watch that is a Family Watch without a separate iPhone use the Blood Oxygen App?

From: https://www.macrumors.com/guide/family-setup/

Family Setup Limitations

Apple Watch Series 6 models that are set up with Family Setup are not able to access the Blood Oxygen app for blood oxygen measurements, a restriction that applies regardless of the Apple Watch owner's age.

Elderly relatives who have an Apple Watch Series 6 may want the Blood Oxygen app, so this is a limitation worth keeping in mind when deciding whether to use the Family Setup feature.

The following limitations also apply:

• High and low heart rate notifications are only available for users aged 13 and older.
• Irregular heart rhythm notifications and ECG are not available.
• Sleep Tracking is not available.
• Fall detection is only available for users aged 18 and older.
• Apple Cash Family is limited to users under the age of 18.
• ‌Apple Pay‌ with a credit, debit, or transit card is not available with Family Setup.
• The Podcasts, Remote, News, Home, and Shortcuts apps are not available.

Battery Life

According to Apple, a watch controlled through Family Setup should last for approximately 14 hours before needing to be recharged. Apple bases that on the following estimated activities:

• 70 time checks
• 45 notifications
• 20 minutes of app use
• 5 minute phone call
• 30 minute workout with music playback

Battery life will, of course, vary based on usage and by each device. The battery life estimates take into account LTE connectivity and operation over a cellular connection.