Image by Michal Jarmoluk from Pixabay

Well, I just had a really stupid Flutter installation on my computer:
Every time I executed a Flutter command, I got the following message:

Waiting for another flutter command to release the startup lock...

In some forums I read that there is a lockfile in the Flutter folder under bin/cache and you have to delete it.

Said, done

Did it help? No, unfortunately not.

I had no other choice than to remove the complete Flutter installation folder and download it again. Then make the new Flutter folder known to the path and execute the old commands again:

flutter channel stable
flutter channel upgrade
flutter doctor

Then I changed back to the project directory and executed the following command

flutter pub get

This command was finished much too fast and flutter packets were still not available. Stupid.
I remembered that there is a .pub-cache folder under the home directory where all the packages are stored. So the whole folder was deleted and the above command was executed again... and Yes,finally... Everything works again.