Re: white mold growing on banana tree and small flies on it and in soil
The little flies sound like fungus gnats, which you get when the soil is staying moist all the time. They won't harm the plant, but their presence suggests you might be overwatering. Cut off any parts of the plant that are completely dead and let the plant dry out to kill the mold growing on it. If the weather is appropriate where you live, getting outside in full sun should help, though don't shock it by taking it from outside and putting it straight into full sun.
Posting some new photos would help us see what is going on with the plant.
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