Does the ECG feature of the Apple Watch 6 work in Lebanon?

No I'm afraid not,here is the list of supported countries;

https://www.apple.com/watchos/feature-availability/#branded-ecg

No,there is no workaround;

For the ECG app to work on your watch the ECG app has to be approved by;

A. the government of the country in which the watch was bought and

B.the government of the country in which you reside.