The problem gets fixed when I go to Settings > Edit Current Profile > Appearance > Font and hit choose. However, this needs to be done every time I launch the terminal application.
I didn’t find anything helpful on the internet. Maybe I am using the wrong search terms? Any help would be greatly appreciated.
This is because the default Konsole profile in Manjaro is root-owned and therefore read-only.
You need to make a copy of the default Konsole profile under a new name, make this new profile the default, and then edit its settings. These will then be saved, because the new profile will then be stored in your home directory and will be owned by you.