Never mind. I deleted the pureforum_skin folder from the server and was able to proceed. Why is it in the archive for 6.10.4 if is empty?

Maybe a error as
a) you can download pureforums_skin from https://skins.b2evolution.net/?s=pureforums&submit=Go&disp=search
b) pureforums (6.8.6) and pureforums_skin (6.7.8) have have the same class name at line 18 so you can only install one of them unless you change the name.

class pureforums_Skin extends Skin
{
	/**
	 * Skin version
	 * @var string
	 */
	var $version = '6.8.6';

pureforums_skin is a newer version so it may be better to download that and delete pureforums

Just made a new topic to highlight the problem
https://forums.b2evolution.net/skins-error-pureforums