One of the new features in QGIS 3.20 is the option to trim the start and end of simple line symbols. This allows for the line rendering to trim off the first and last sections of a line at a user configured distance, as shown in the visual changelog entry.
This new feature makes it much easier to create decorative label callout (or leader) lines. If you know QGIS Map Design 2, the following map may look familiar – however – the following leader lines are even more intricate, making use of the new trimming capabilities:
To demonstrate some of the possibilities, I’ve created a set of four black and four white leader line styles:
You can download these symbols from the QGIS style sharing platform: https://plugins.qgis.org/styles/101/ to use them in your projects. Have fun mapping!