Good, because that is very bad advice. orzechod already gave you a link to the manual, but the upshot is that basically every emacs command already breaks the undo into segments. Arrow keys invoke commands to move the cursor around, and backspace and return invoke commands as well, so you don’t need to add anything to your config to get most of what you want.

The only difference is that the default Emacs config groups up inserted characters into segments of 20 characters, instead of splitting them on punctuation and spaces. Getting that last bit is harder, so you might actually prefer to live with it. You should be able to do it with advice on self-insert-command, but I would have to do a little research and try it out before I would be confident in my answer. (I am 90% sure that you can set a variable to control whether the current command should be amalgamated or not, but it’s been years since I last looked at how undo is implemented.)

I should also point out that brackets might or might not be amalgamated depending on other choices you might have made. For example, if you use a minor mode that automatically inserts the closing bracket when you type the opener, then it won’t be amalgamated because that is invoking a command rather than merely inserting a character.