PranavJadhav
edit vendor/flarum/flarum-ext-tags/js/forum/dist/extension.js
find
tagIcon(tag, { className: 'Button-icon' }),
change
tagIcon(tag, { className: 'Button-icon' }),
this.props.children
to
tagIcon(tag, { className: 'Button-icon' }),
this.props.children,
' '+ tag.discussionsCount()
But I don‘t recommend using it,
It's count is not accurate (when you change the tag of the discussion).