How to avoid error message "no main manifest attribute, in MyApp.jar"?

Question

When I try to run a (Vaadin Spring Boot) application I created in Intellij Idea:

java -jar MyApp.jar

... I get the following error message:

"no main manifest attribute, in MyApp.jar"

I tried several of the solutions to this problem provided in posts pertaining to the same problem but I keep getting this error message.

Does anybody know a solid way to avoid this error message?

By the way:

the manifest file does exist:

and has the following content:

Manifest-Version: 1.0
Main-Class: com.my_app.MyAppApplication

************************************UPDATE***********************************

MINIMAL EXAMPLE:

Using SpringInitializr (https://start.spring.io), I created a mini-app called minimalExample2. The SpringInitializr tags used are:

After creating a jar-file, the project-structure looks as follows:

The content of the MANIFEST.MF file is the following:

Manifest-Version: 1.0
Main-Class: com.example.minimalExample2.MinimalExample2Application

When I want to run the app using

java -jar minimalExample2.jar 

... I get the following error message:

"no main manifest attribute, in minimalExample2.jar"

You can easily replicate this app in a few seconds by selecting the two tags "Web" and "Vaadin" in Springinitializr and then clicking on "Generate Project".