Mortallylive

Разобрался, решил залезть в исходники Tinymce в виджеты:

def render(self, name, value, attrs=None, renderer=None):
        if value is None:
            value = ""
        final_attrs = self.build_attrs(self.attrs, attrs)
        final_attrs["name"] = name
        if final_attrs.get("class", None) is None:
            final_attrs["class"] = "tinymce"
        else:
            final_attrs["class"] = " ".join(final_attrs["class"].split(" ") + ["tinymce"])
        assert "id" in final_attrs, "TinyMCE widget attributes must contain 'id'"
        mce_config = self.get_mce_config(final_attrs)
        mce_json = json.dumps(mce_config)
        if tinymce.settings.USE_COMPRESSOR:
            compressor_config = {
                "plugins": mce_config.get("plugins", ""),
                "themes": mce_config.get("theme", "advanced"),
                "languages": mce_config.get("language", ""),
                "diskcache": True,
                "debug": False,
            }
            final_attrs["data-mce-gz-conf"] = json.dumps(compressor_config)
        final_attrs["data-mce-conf"] = mce_json
        html = [f"<textarea{flatatt(final_attrs)}>{escape(value)}</textarea>"]
        return mark_safe("\n".join({escape(value)}))

Возвращало

html = [f"<textarea{flatatt(final_attrs)}>{escape(value)}</textarea>"]

вместо {escape(value)}, по каким неведомым причинам это было сделано, хз.