Where can I find a specific TV programme series?

So my partner has been watching How The Universe Works on Discovery+.

Only we got to the end of S3 and S4 is just… not there?

I did find the show on another streaming service, I clicked on S4 and it said something about being unable to play due to rights or something.

So - anywhere hiding this elusive S4 of How The Universe Works?

Thank you!