How to add "_" character to RewriteCond in .htaccess?

Question

PHP

Currently there is this rule:
RewriteEngine on
RewriteCond %{REQUEST_URI} \/([0-9a-z\&\=\.\[\]\{\}\%\-]+)$ [NC]
RewriteRule ^ (.*) /hello.php?query=%1 [L]
It, as experts have already understood, sends from /hsdfs to /hello.php?query=hsdfs
hsdfs is a string that can contain characters 0-9, az, &, =, etc...
I need to add one more character "_" to these characters. But when I convert the second line like so:
RewriteCond %{REQUEST_URI} \/([0-9a-z\&\=\.\[\]\{\}\%\-\_]+)$ [NC]
or so
RewriteCond %{REQUEST_URI} \/([0-9a-z\&\=\.\[\]\{\}\%\-_]+)$ [NC]
I get 500 error...
How to achieve what you want result?

Answer 1

Resolved like this:
RewriteCond %{REQUEST_URI} \/([a-z0-9_[\]{}%&=-]+)$ [NC]

Answer 2

According to my mystical rule, underscore cannot be at the beginning or end of a list of characters. try moving it 1 character to the left. It should work.
upd0 : maybe I'm driving