Windows excel from encryption point of view its fully secure after 2000. Its encrypted with AES 128 bit, generated from the password you have provided. The issue is the strength of your password. There are lots of online sites that can tell the strength of your password.
Since your file is offline, hash can be extracted and offline brute force can be made. If your password is just a word and few number it will take minutes to calculate. But if its long, it can never be found out.
I extracted the hash and the salt from your excel and run it on john for few minutes couldnt find your password. Here is your hash for john the ripper.
Security [login to view URL]:$office$*2010*100000*128*16*86f46c29f8603557e25e5a248d854eca*fa4033c2f2d01c892ca5948461dc5254*2e5e6ad677c61aa4b4712b8b360361733b014133dfb8b2b7d91b7a50f75120cd
With 2 CPU 2 Core vm machine i can try 55 guess/second. So depending on password length and complexity guess how long it will take to calculate.
With 8 Core intel 7 machine can try 175 guess/second.
Hiding a sheet doesn't add any security in excel, just if you want to share something people but there are some confusing thing you may want to hide them. Other than that they can easily be exposed. Just running a macro
Sub macro()
Dim ws As Worksheet
For Each ws In [login to view URL]
[login to view URL] = xlSheetVisible
Next ws
End Sub
or more easier one
Sub Macro()
[login to view URL] = True
End Sub