MuseScore provides brackets and a curly brace in the Brackets palette (Advanced workspace).
When a new score is created using a template, MuseScore automatically sets the correct brackets.
To add a bracket or brace to systems, use one of two methods:
When you first apply a bracket it only spans one staff. To extend to other staves:
The default thickness and distance from the system of brackets and braces can be adjusted in Format→ Style... → System.
In the System Brackets section, you can set the properties for the brackets in the two boxes on the left, and the properties for the braces in the two boxes on the right.