Tagging in that area is dubious anyways. Sandbox visual novels are not visual novels, in a stricter sense. In a less strict sense, anything with characters that give dialoge could be considered a vn.

So by searching for sandbox you already filter out things that do consider themselves visual novels. But games might tag vn as well, because they use that as a base engine.

Speaking of engines, you could try searching for engines. There are less vn in unity for example.

But if you trust the tagging of the devs, you can exclude a single tag from search by adding something after the search url. See those sticky threads about multiple exclusion or similar threads. 

?exclude=tg.tag

with tag being the tag as it appears in the url, if you were to seaarch for it.

If you had posted in the right category from the start, you might have spotted this recent topic for example, because people ask all the time.