"开放式画风的" can be translated as "with an open or free-style painting approach" or more concisely as "featuring an open painting style" in English. Here are a couple of example sentences to illustrate its usage:
1、 This artist is known for his works that feature an open painting style, allowing viewers to interpret them in their own unique ways.
（这位艺术家以其具有开放式画风的作品而闻名，允许观众以自己独特的方式解读它们。）
2、 The exhibition showcases a variety of artworks, including some with an open or free-style painting approach that challenges traditional artistic norms.
（这次展览展示了各种各样的艺术品，其中包括一些具有开放式或自由式画风的画作，它们挑战了传统的艺术规范。）