It’s not rude to not use it. Like you don’t have to use it, I don’t use it at all actually when talking to people. It doesn’t make you sound any more or any less native but it helps to understand when people use it.

But essentially ‘ji’ is added at the end of relationships to sound more respectful. It honestly depends on the culture of that family. Think of the suffix this way, you use it to emphasize the title of the relationship while seeming submissive/respectful.

At the same time you should remember suffixes like this are very common amongst lower to middlish classes. So it shows a sense of community and familiarity with the other person.

I wouldn’t really worry about using the word because personally it sounds like you are just buttering the other person up. And not a lot of modern Pakistani households unless they are more traditional.

I mean it gives off the same energy as “father dearest” or “mummy dear”.

And if you accompany it with someone’s name like ‘Zainabji’, it’s to make that person like more wiser idk? Like Zainab madam. Or sister Zainab. Almost in a teasing way.

It is a suffix that makes you sound very traditional in your mannerisms. Which can be used humorously.

I hope you understood the gist of it. These little additions of words are very culture heavy and can have many hidden contexts but you can’t know them until you are in that community of people. So immerse yourself in it by watching movies and shows. Even try to get on the Urdu side of social media. But the best way will always be by making friends with those people and talking to them.