Blood Oxygen and ECG not available

Is iOS 14.4 installed on your iPhone?

Is watchOS 7.3 installed on your Watch?

If not, first update your devices(s).

Make sure your Settings > General > Language & Region are set correctly.

FYI:

1. Blood Oxygen app measurements are not intended for medical use, including self-diagnosis or consultation with a doctor, and are only designed for general fitness and wellness purposes.
2. The ECG app and irregular rhythm notification require the latest version of watchOS and iOS, and are not intended for use by people under 22 years old. The ECG app is available on Apple Watch Series 4 or later (not including Apple Watch SE). The irregular rhythm notification is not designed for people who have been previously diagnosed with Afib.

Still no joy, the Watch may be imported from overseas.

Check iPhone's Watch app > My Watch > General > About > Model > tap here to see number starting with A????

Compare it with this link => Identify your Apple Watch - Apple Support

Tell us where you are using the Apple Watch?

And which country was the Apple Watch bought?

The options are not available everywhere.

See country list that support ECG => watchOS - Feature Availability - Apple

And Blood O2 => watchOS - Feature Availability - Apple

Note: Blood Oxygen app is not supported on an Apple Watch SE

But you didn't buy Watch in South Africa, did you?

The options depended on

1. Where the Watch was sold (not illegally imported)
2. Where the Watch is used.

You're welcome, enjoy.