IntelliJ unable to run: main class not found. Terminal runs the class just fine

After extensive research through Google, Stackoverflow and peers I am still unable to solve the below stated issue.

IntelliJ is unable to locate any main class of whatever file I choose:

Error: Could not find or load main class nl.sam.inventory.InventoryApplication

I have followed the answer which was posted on SO: Error "ClassNotFoundException" in IntelliJ IDEA

My main class:

package nl.sam.inventory;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class InventoryApplication {

    public static void main(String[] args) {
        SpringApplication.run(InventoryApplication.class, args);
    }
}

My run settings are left as default (IntelliJ picked these up).

My project structure: Project Structure

If I left anything out please state so.

I have verified I have a JRE (11) and JDK (11) installed and working on my machine. In a terminal the program runs just fine: in IntelliJ I get the aforementioned error.

Edit: I use Maven for project management. A project without maven shows the same behaviour.