If it's showing those duplicates AND your website does in fact show up for both URLs without redirecting, then yes that's something I've come across before and that's something for you to fix.

Each page on your site should show up for the www or non-www but not both. Choose whichever one has the most Domain Authority (Moz metric) and redirect the other version to that. Your developer should know how to do so. WWW is often recommended the most.

Paste "site:example.com" (replace example with your name) into Google search to see what version of your URLs is indexing the most.

It's a weird technical thing, but it's worth making sure you have it done right. It's most likely not going to be a game changer, but it will help your site to a small percentage to have that properly in place.

Happy to answer any other questions on this!