I've noticed many similarities for example:

• the lion symbol on the suits of armor looks exactly the same as Harry Potter's Gryffindor lion

• there are 7 books in the Narnia and Harry Potter septuplegies




• the main characters are part Muggle or full Muggles

I'm sure there is more I haven't listed, But, is Narnia the same fictional universe as Harry Potter or a different universe entirely?

No. In the world of Narnia magic can be learned (and used in a haphazard fashion) by those without magical blood. In the world of Harry Potter, it's exclusively used by humans with magical ancestry.

"I see," she said scornfully, "you are a Magician—of a sort. Stand up,
dog, and don't sprawl there as if you were speaking to your equals.
How do you come to know Magic? You are not of royal blood, I'll
swear."

"Well—ah—not perhaps in the strict sense," stammered Uncle Andrew.
"Not exactly royal, Ma'am. The Ketterleys are, however, a very old
family. An old Dorsetshire family, Ma'am."

"Peace," said the Witch. "I see what you are. You are a little,
peddling Magician who works by rules and books. There is no real Magic
in your blood and heart. Your kind was made an end of in my world a
thousand years ago. But here I shall allow you to be my servant."

_{^{The Magician's Nephew - CHAPTER VI}}

That in itself indicates that these are not set in the same fictional universe.

With regard to the similarity of the lions, you should be aware that both the Narnia shields and the lion depicted on the Gryffindor banners are not original creations. They're representations of a heraldic "Lion Rampant" which goes back to at least the 1400s (and before). Most depictions after the 1800s follow an extremely similar pattern to those seen in various fantasy books/films including Narnia and Harry Potter

_{^{Arms of Strange and Talbot - Catalogue of the Heraldic Exhibition in London, 1894.}}

You might wish to note that JKR spoke on the key differences between the world of Harry Potter and Narnia

I found myself thinking about the wardrobe route to Narnia [in the C.S.
Lewis series including The Lion, The Witch And The Wardrobe] when
Harry is told he has to hurl himself at a barrier in Kings Cross
Station - it dissolves and he's on platform Nine and Three-Quarters,
and there's the train for Hogwarts. Narnia is literally a different
world, whereas in the Harry books you go into a world within a world
that you can see if you happen to belong. A lot of the humour comes
from collisions between the magic and the everyday worlds. Generally
there isn't much humour in the Narnia books, although I adored them
when I was a child. I got so caught up I didn't think C.S. Lewis was
especially preachy. Reading them now I find that his subliminal
message isn't very subliminal at all.

Really, C.S. Lewis had very different objectives to mine. When I write, I
don't intend to make a point or teach philosophy of life. A problem
you run into with a series is how the characters grow up ... whether
they're allowed to grow up. The characters in Enid Blyton's Famous
Five books act in a prepubescent way right through the series. In the
Narnia books the children are never allowed to grow up, even though
they are growing older.

_{^{"The story behind the Potter legend:
JK Rowling talks about how she created the Harry Potter books and the magic of Harry Potter's world,"}}

No

To start with if anything was going to be in the other's universe Harry Potter would be in Narnia's as The Lion, the Witch and the Wardrobe was originally published in 1950 and Harry Potter and the Philosopher's Stone was originally published in 1997.

Even beyond that the "similarities" you've listed aren't really similar:

• 
  

  the lion symbol on the suits of armor looks exactly the same as Harry Potters Gryffindor lion

  
  
  

  They're both just lions, there are only so many ways to depict them.

  
  


• 
  

  there are 7 books in the Narnia and Harry Potter septuplegies

  
  
  

  I'm not sure how a book series having the same amount of books in any way dictates that the works are in the same universe.

  
  


• 
  

  the main characters are part Muggle or full Muggles

  
  
  

  In Harry Potter sure and even then not really but in Narnia I don't think you can call them Muggles at all.

  
  

No.

The Harry Potter universe and the Narnia universe are separate universes.

There are many in and out of universe things to, so to speak, prove this, but I'll only list a few.

In-universe.

• Harry Potter takes place entirely in our world, and the magical parts are "simply" hidden from the mundane parts. The Narnia Universe, however, involves travelling to other worlds/planes.


• There are no talking animals in the Harry Potter universe, while there are many of them in the Narnia Universe.

And, more importantly, Out-of-universe:

• Had Harry Potter universe and the Narnia Universe been the same, either J.K. Rowling would be swimming in law suits or the Lewis estate would be swimming in (even more) money, or


• We would know about it. Unequivocally.

No

First of all, IIRC Rowling never mentioned being inspired by Lewis. Moreover, Narnia universe was created something like 50 years prior to Harry Potter universe, so technically it would be other way round (but it's not really the case).

Also, all of the "similarities" you list seem to be coincidental or not a similarity at all.

There is also different underlying references throughout the series: while Harry Potter's arc with Voldemort and Death Eaters has a lot in common with Hitler and Nazi's view of the world, Narnia has more of a Christian theme.