a matter of (personal) opinion / taste

/ɐ mˈatəɹ ɒv pˈɜːsənəl əpˈɪniən tˈeɪst/

/ɐ mˈæɾɚɹ ʌv pˈɜːsənəl əpˈɪniən tˈeɪst/

something about which people have varying opinions

Examples

1. Art is very much a matter of taste.

2. Choosing the best ballplayer of all time is really a matter of opinion.

3. But without regulation, medical research, and clear consumer knowledge, the human value of CBD oil will, for now, remain a matter of opinion.

4. Although, tiny is a matter of opinion.