The issue is from Substeps IntelliJ Plugin that IntelliJ suggests you install when it locates a .feature file inside your project. Just ignore this extension when it pops up or uninstall if you already have it. Cucumber for Java and Gherkin should be enough.
Spring Boot property resolution property order is described here. Use of application.properties and application.yaml is not expected. Use one format or the other but not both. Whichever one you use will be handled at position 12 or 13 (depending on whether the file is packaged in the application JAR or not) in property precedence order. … Read more
I had this same problem, and @AniaG’s solution in the comments worked for me. Right-click src folder Mark Directory as > Sources Root