In the library tab, it is possible to delete files from the drive using just pressing the del button.
I don't want my most important files to be deleted like this, but how can I fix it?

in settings-files make sure that the 'send files to trash instead of deleting' is on
at least then if you accidentally delete something it is in the trash where you can bring it back.

The feature is enabled, but I have more than a terabyte of information, so it looks like it might not help.