There is no such thing as "free" unless the original author released files under CC0 or Public domain. The rest of the ecosystem is a legal minefield even for kids kit-bashing a project for fun.
replyWe spent around $3k conducting a survey of the Blender ecosystem for a game dev project about 2 years ago, and continue to monitor the situation every update. A rather sobering experience in some ways.
Would recommend Poly Haven as the plugin is not required to access their free assets, but it is usually a good idea to support people that make things easier for everyone. =3