Why Apple Watch doesn’t ring ?

Using the Watch app on your phone, check these settings:

1. In Sounds & Haptics

Check the Alert Volume slider, turn it up?

Check the Silent Mode toggle. If it's green, turn it off. Exit page then...

2. Scroll down the screen until you get to Phone and then click on it.

Is it set to "Mirror my iPhone"?

Is the Ringtone toggle Green? If not, turn it on.

Also, check for updates. Your watchOS looks like it's behind. It can be updated as high as watchOS 8.7.1 (this is the last update for Series 3 watches)

Let us know how this goes and if you need more help.