Why we must have a confident mind? “Here, bhikkhus, some person has a confident mind. Having examined his mind with my mind, I know that if this person were to die at this time, as if carried there he would be placed in heaven. What is the reason for that? It is because his mind is confident. It is because of the mind’s confidence that some beings here, when the body perishes, are reborn after death in a good bourn, in a heavenly world.”
Iti 21

Why we must have a confident mind ? What is a confident mind according to the Lord Buddha ?
What are the differences between confident and

Conceit
Clinging to a view
What is a confident mind according to the Lord Buddha?


From your quote, confidence is translated from the pali word pasannacitta. Pasannacitta literally means devoted mind, and can be interpreted as a person having faith (saddha).

https://www.wisdomlib.org/definition/pasannacitta


  Why we must have a confident mind?


It is considered one of the five mental faculties/indryas that aids progression towards enlightenment.

https://www.accesstoinsight.org/tipitaka/sn/sn48/sn48.010.than.html


  What are the differences between confident and conceit


Conceit (mana), is a cetasika with attachment/lobha as base. Mana means that we are attached to the misconception that there is a self that is superior to others.


  What are the differences between confident and clinging to a view


Primarily the difference is the fruit of their karma. Besides being a mental faculty mentioned above, AN 5.38 also lists five benefits of saddha for laypersons, for instance.

https://www.accesstoinsight.org/tipitaka/an/an05/an05.038.than.html

Clinging to a view, on the other hand is simply not beneficial, and perpetuates dissatisfaction. Your comparison with conceit seems like an appropriate example.