How do I know whether or not I'm using My Photo Streams?

If the option for Photo Stream is not in your settings on your devices, then there is no way that you could be using it if there is no way to enable it.

Apple ID’s that were created after a certain date no longer had the option to use Photo Stream. My wife and daughter created Apple IDs in 2018 and there was no option for them to use Photo Stream.

You are using iCloud Photos, not Photo Stream.

One other way to be certain is to go to Settings>Photos. If you have the option to use Photo Stream you will see it in there. If you do see the option, it is most likely disabled because you are using iCloud Photos. I don’t think you can use both at the same time.

Thanks for the info.

In the spirit of absolute paranoia, my settings screen doesn't include the option: My Photo Stream. It's not disabled. It's just not there. (See the screen shot.)

And, I have an ancient Apple ID, so I'm pretty sure I did have access to My Photo Stream. (I sorta remember the words.)

Do I know without a doubt that I have no leftover My Photo Stream?

Thanks!

Please see the pic below which is self-explanatory.

Yes. A safe conclusion, I would say.

If you recently created your Apple ID, My Photo Stream might not be available. 

Thanks.

As you said, the option is not there.

I think my paranoia is assuaged.

Thanks again!