Is it permissible to create a website to sell website templates, knowing that these templates might be used for permissible or impermissible matters, such as posting pictures of unveiled women or speech that violates Sharia?

It is permissible to sell molds that can be used for both lawful and unlawful purposes, unless it is known or highly probable that the buyer will use them for impermissible acts. If it is highly probable that they will be used for disobedience, then the sale is prohibited. However, if there is uncertainty, the default ruling is permissibility. There is no obligation to investigate the buyer's intention, to avoid undue hardship.