Moot and Moat are easily confused words.
The spell-check application of most word processing software programs would not catch a slip-up of these two words. Spell-check is looking for words that aren’t in its dictionary, and words that resemble words in its dictionary but are possibly spelled wrong. Spell-check isn’t perfect. It doesn’t know and can’t guess what word you wanted or what word you meant, it can only judge the words on the page. If you used words that are all spelled correctly, it gives you a pass anyway. Similarly, autocorrect on mobile phones might suggest one word instead of the other, it would be easy to do since both words start with “m-o.”
Moot (pronounced “moott” rhymes with “boot”) is an adjective. It means means futile effort, a foregone conclusion.
Moat (pronounced “moht”, rhymes with “boat”) is a noun, surrounding a castle and meant as a protective boundary from invaders.
The following story uses both words correctly:
King Mojin overthought putting a moat around his castle. Once the invaders arrived, he had just decided it was a good idea. By this time, the point was moot.