SUMMARY
All the messages I receive are encrypted with OpenPGP and I realized that they are not being displayed correctly.

The lines are not being break automatically, and kmail is displaying a bar at the bottom so that the user can see the content of the message. This is very annoying especially when the message is large and I have to keep going back and forth to be able to read it.
https://i.imgur.com/IoncNor.png

Decrypting the email in another folder solves this. The email is displayed correctly with the necessary line breaks.
https://i.imgur.com/MhaC5ik.png


STEPS TO REPRODUCE
1. Open an encrypted email with a big text 
2. You will see that the lines are not being broken
3. Decrypt that same email to some other folder
4. Now the email will be displayed as it should


SOFTWARE/OS VERSIONS
Operating System: Arch Linux
KDE Plasma Version: 5.19.3
KDE Frameworks Version: 5.71.0
Qt Version: 5.15.0
Kernel Version: 5.7.7-arch1-1
OS Type: 64-bit


ADDITIONAL INFORMATION
This happens in messages with and without HTML