“Maybe” may be my biggest pet peeve of late. It shouldn’t be this hard to get right.
Perhaps we need a tip, so try this one: Think of the word “might”. If you can use might instead of may, then you should be typing the two-word may be, not maybe.
“I might be late to the party because my train is delayed.” or “That kitty might be the cutest animal ever”. In both these sentences, you could use “may be”.
Conversely, you wouldn’t say “Might be I’ll go to the party, if my train gets here in time.” You would say “Maybe I’ll go to the party.”