Could someone help me with this breadcrumbs error in GSC?

Missing field 'itemListElement' Items with this issue are invalid. Invalid items are not eligible for Google Search's rich results. I tried out a few plugins in Wordpress, which didn't work (Breadcrumb - Pick Plugins, Breadcrumb NAVxt and Breadcrumb Block), however none worked due to the theme, and I undid changes and deactivated. However now I'm getting these errors in GSC. Would this be due to the changes, even though I deactivated the plugins? Or is this referencing the Structured Data and is just a coincidence? Sorry I am very new to technical SEO - any help appreciated!