I can reproduce this on PS5 offline mode. I haven’t tested it on online mode.
The maximum number of characters in offline is 30. However, if you close the game and open it again just 28 characters are shown. The additional characters are not deleted, just hidden. If you delete some characters and reload the game, the hidden characters are shown again. The hidden characters are always the ones that were used the longest ago.
The hidden characters do not count towards the total of offline characters. If you have 30 characters and reload the game, just 28 characters are shown and you can actually create 2 more characters. You can repeat this process multiple times. I haven’t tested if there is an actual limit.