Verbal | "maybe" vs "may be"

1)Can somebody explain the usage difference between"maybe " and"may be "

2)there are many rumours about "maybe" in many gmat forums
that its usage is banned in gmat.
so if you see "maybe" in any answer choice. just cross it. because its unidiomatic
Is it true ?

3) if possible please explain the following words in their usage as well and difference in theirusage
"probably ",may be quot;,"maybe quot;,and"perhaps quot;
...

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