Hi there!

I don't believe there is any hard and fast rule for a minimum number of listings required for a keyword to be eligible for Shopping. I don't believe Google has never publicly said so, but I would imagine it's more to do with search volume.

If you really believe in the keyword, I'd suggest giving a go with exact match bidding through Search. If you can get it anywhere near profitable using Search, you can be confident it'll be profitable using Shopping and it's worth your time.

What's the monthly search volume? If it's significant, then I'd reach out to Google support and ask why it's not appearing for Shopping.

Either way, it's worth keeping the campaign live - if you have decent search volume Google will eventually decide it's worth a go on Shopping. Even if the term is not appearing, it may appear for others that are similar.

I'd also keep an eye on the time since launch. Usually with a new campaign and product on Google Shopping it can take up to two weeks (at least!) before you see any meaningful impressions.

I'd also recommend looking into Bing, is Shopping enabled for that term over there?