I have zero interviewing experience as an applicant, but I've hired some freelance developers before. So take my feedback with some grain of salt.

I imagine they will try to understand the following things:

• Do you have the relevant technical skills? Whether you coded your own thing or within a business doesn't matter for this part. Expect them to ask about your decision making. Why this framework over another. What trade-offs did you make and why. Etc.
• Are you able to pick up new technologies and ways of working? What are some of the recent things you've learned?
• Do you work well with others? You mentioned not having coded "professionally", but only your own products. Have you worked with other people in another capacity? Can you share some examples and possibly any conflicts and how you resolved them?
• Related to the above: Are you able to clearly communicate technical stuff? What about talking to non-technical people?

I also suggest reading up on the company, which technologies they use, and maybe check some of the LinkedIn profiles of employees to see how they describe their roles within the company. That might give you some more things to research.