What did Roger and Anita in 101 Dalmations do for income?

Roger is a songwriter in most versions of the story. This is a bohemian profession in line with his Bachelor lifestyle. In the animated film, and book and others, Anita is never shown as having a job, as it was not typical for a single woman to work at the time. She likely would have lived with her parents until she got married, hence becoming a House Wife as a profession. At the time, Roger would be expected to be the sole breadwinner. They are comfortably working to lower-middle class. As the story doesn't focus on them, and is meant to be a heartwarming tale, there is no need to introduce the pressure of living paycheck to paycheck, or have Roger and Anita worrying over selling a song or being commissioned.

In the live action film, Anita is now a Fashion Designer working for Cruella instead of just being her friend. Roger has been changed to be a Video Game Designer, still a bohemian artistic role in keeping with his original profession. As it is a modern retelling, the dual income working class life style is used. It was much more common for both to work to afford their lifestyle in 90/2000s.

As to Cruella's comment about not affording the dogs, while Anita and Roger live a comfortable working class life, the expense and time of multiple dogs could make that harder. But Cruella is also very very... classist and overall not a kind person. She assumes Anita is poorer than she really is because Cruella thinks she's better than Anita. She also has a one track mind and is trying anything to make sure she gets the fur coat she wants. It's not that Roger and Anita are actually poor, but the added cost of multiple dogs could be an issue and Cruella is attempting to capitalize on it.

In addition to @cde's answer, in the animated version the story takes place in the 1960s.

Roger's job isn't really looked at closely because he's not a key part of the story. But as a "freelance song writer" he probably has had, in the past some success in selling his work.

At the time of the story he has writers block and the new couple (Roger and Anita) are struggling with their new situation, and the lack of income due to his writers block, but there also very much in the "Honeymoon phase"

Keep in mind that a freelancer, even today, doesn't get money on Monday and spend it on Tuesday. You have to store some for the times when your not working. Roger and Anita seem to be living off that (past) income.

In the 1960s version Cruella is a rich, snobby, well I can't think of a kid friendly word for it. She would think that Rodger and Anita "Can't feed themselves" because they were eating out each day at the most expensive and most popular establishments.

Also as pointed out, it's basically a feel good movie about the dogs. So while it's important to remember "That if she doesn't scare you no evil thing will." It's also not important to know that their (Roger and Anita's) version of struggling was likely just changing from going out Fridays and Saturdays to only going out Fridays.