Depends on why you are saying it. Adding the adjective means the person is not trying to change their status. Another way to phrase it , is ‘an avowed bachelor’

He’s single by choice. has a similar meaning Using the word ‘bachelor’ sounds a bit imprecise these days. It’s the name of a TV show which gives the word associations beyond ‘unmarried man’

"Confirmed bachelor" is an old-fashioned term and carries certain nuances. Check out the Cambridge Dictionary online for some examples. Even 'bachelor' is no longer in common use in Ireland to describe the single status of a man (except on a marriage certificate). I've consulted my English friends and they don't use it either, instead favouring 'single' or 'unmarried', depending on the situation.

The term "confirmed bachelor" traditionally refers to a man who is not married and is often used euphemistically to suggest that he may be intentionally avoiding marriage. However, the term can be considered somewhat outdated and may carry connotations that some people find old-fashioned or stereotypical. Using "bachelor" alone is a more neutral and modern way to refer to a man who is unmarried. If you want to be respectful and avoid potential outdated stereotypes, it's generally better to say "bachelor" without adding the qualifier "confirmed." Additionally, it's important to keep in mind that individual preferences vary, and some people may not appreciate labels or assumptions about their marital status. When discussing someone's relationship status, it's always considerate to use language that is inclusive and non-judgmental. If possible, you can simply refer to someone as "single" if you need to convey that they are not currently married.

A “Confirmed bachelor ” is a man that declares he has no intention of marrying. A “Bachelor “ is a man who isn’t married. Whereas “confirmed a bachelor “ means you’ve checked and he’s a bachelor.