Hi @MAIA1, glad to have you with us.
In order to help answer your question, where did you obtain the Klarna Checkout module from? Let me know and I should be able to offer some further advice.
@MohamedSuliman had the same issue (found here) a few days ago with a different module that he was trying to install via the Magento Marketplace. We discovered that the version on the Marketplace was an old version that possibly wasn’t compatible with Magento 2.3. So, instead he installed it via composer directly from the developers own repository (which was up-to-date).
Installing/Updating Modules
Personally, I always use Composer (when possible) to install and update modules. The process is quicker and tends to be more reliable. Obviously, this method isn’t for everyone as the Command Line Interface can seem overwhelming at first.
Permissions
777 is never the solution to a problem. If you need to change folder/file permissions to 777 then there is a deeper issue somewhere else. The consequences of 777 can easily result in malicious activity to your website resulting in either the destruction of your store - or worse - a breach of your customer data.