Todor Nikolov writes:
Hey Blender community,
Blender 2.91 introduced a few (seemingly) minor interface changes in Weight Paint mode.
Namely, the old "X-mirror" option was moved and renamed.
These changes can be confusing to both new and experienced users alike.
To complicate things further, the changes in 2.91 created inconsistencies which will be fixed in the upcoming 2.92.
I cover all of that in the video below.
If you do any type of weight painting, especially for characters, make sure you understand what has changed.