That won't work for local changes to files that are legitimately committed in the repo. Like if you need to set your local database, or your own dev hostname in config, for example.
If my local setup requires me to ignore changes in checked-in files, I usually find that I need to handle configuration more cleanly.
(I did work on a project that made use of git update-index - this was a terrible mistake and caused pain every time we needed to update the config file in the repository. Please never go down this route!)
Most places I've worked at have created tooling that more or less merges the two - sane defaults and non-sensitive values go into a `.env` file of some kind (.env, .env.development, whatever), and then a tool merges a subset of that config from a remote store which contains the stuff you don't want committed in the repo.
Usually used for connecting to a remote dev or staging instance if you can't or don't want to run the entire stack locally.
There's .git/info/exclude, but that has some kinda large surprises if it excludes a tracked file and I don't recommend anyone use it unless they know what to look for and can always remember what they've excluded.
Git will fight you if you ignore .config files which are actually used.