I print the matrix. It shows [[5]]. My code returns 5.

I get the error, should be 4.

[[5]]
[[5]]
5.0
✘ Determinant of a 1 x 1 matrix yields the value of the one element: 4 should equal 5

That was fun. I was glad not to find any solution that was way shorter than mine :)

This was great. My first attempt was a brute force approach. Took forever to get right, very difficult, then the runtime was too long. Then I rethought it, taking a more clever approach. Very easy to code.

I like how the brute force approach makes this seem hard, but the clever approach makes it easy!

Python version of Mykhailo_Yuschenko's question

print htmlize(cells)

shows

Got
░░░
░░░
░░░
instead of
░░░
▓▓▓
░░░

Know how to fix this for Python?

This is expected.

IMO the checking of None ans nil, and non-integer characters detracts from the spirit of the problem.