Probably and probability 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.
Autocorrect suggests words that start with the same letters. It’s suggesting what word you may want to save time, but quite often, its suggestions are pretty off base. They don’t help you out, but they do make you laugh.
Probably is an adverb. It modifies a verb to indicate that an activity is affirmative or likely to take place. Probably followed by not means that an activity is negated, or it will not take place.
Probability is a noun. It means the ability to guess what will happen in the future based on numerically measuring, or by studying previous results of similar events. Numerical probability is a big part of Statistics.
The following story uses both words correctly:
Ptolemy was growing really tired on waiting for his college acceptance letters to come in at the mailbox. The postman gave the same answer every day, “Not today but probably tomorrow.” What were the odds he would say the same thing every day for the next month? The probability was very high.