Looks ok by inspection, not tested.
A couple of suggestions for improvement:
1. include `<>` if the `brace_match_ltgt` is set
2. the search for `]})` will find those characters in comments and strings so the selection is probably not what the user intended. Not sure how to cure that though 3. will mitigate it somewhat.
3. check if the cursor is in a position where a pair of brackets are already highlighted and use that pair instead of searching
If you don't want to do these in this PR thats fine, please copy them into a future improvements issue.