Humor and humour are two spellings of the same noun or verb. The spelling depends on the type of English.
In American English, you use “humor.”
In British English, you use “humour.”
Australian English mostly follows British English guidelines, so humour is correct.
The same difference applies to similar words, such as “behavior or behaviour,” “labor or labour,” “favor or favour,” “favorite or favourite,” “color or colour,” and “honor or honour.”
It’s important to choose one and use it consistently. The QuillBot Grammar Checker can help you with this.