I have twins who are nearly 5 and just started reception
I've always read lots of books to them and childminders did a bit of letter sounds with them but rather haphazardly so they've had no real 'teaching' until they started school mid sept
One is already able to blend and if he sees a word, eg cat, will immediately say c-a-t, cat. He can read simple books if they have mostly 2-3 letter words and single sounds (they haven't learnt things like sh/ch etc yet) and is super keen (when the teacher left the same words to learn in his word book for 2 weeks he asked me to print out some new ones for him because he was bored of the same old ones which he already knew!) I am doing lots to encourage him because he's so keen and I want to capitalise on that.
The other by contrast will firstly just guess at random words, then when encouraged will (rather grudgingly!) say c-a-t and then when I say what word does c-a-t spell, he'll say (for example) goat! Or whatever else comes into his head at the time! Bless him, just not got a clue yet ??
With him I am reverting to just reading lots of books and pointing out letters and sounds in everyday life, he's clearly not ready for more yet and I don't want to put him off reading for life
I would agree with everyone else here, sounds like your little one just isn't ready to read/blend yet so maybe take a step back and just enjoy reading and playing letter/sound games together and when he's ready he'll have a really good grasp of the basics ??
For what it's worth, I was reading at 3 because I was interested and wanted to, my sisters didn't read until closer to 5-6yrs - hasn't made a jot of difference to our adult lives ??
oh, and banana is tricky because it has two different 'a' sounds in it - short 'a' in ban but long 'ah' in nana - so very confusing if you are just starting out. If you do want to persevere with reading, maybe start with easier words - if you google phonics programmes (we use Letters and Sounds at school here so I googled that) you will find lists of words to start with which use the letter sounds in the order they are taught in school. Eg they start learning S, A, T, P, I, N - so example words might be sat, at, tap, in, it etc....