Two switches in Configurations › Online Catalog › Display Options. Flip them and you're done — nothing to save.
Shows customers how many units you have.
Where it appears: on the product page, right below the buy button, as Stock: 12. If the product is sold by fraction, the number also shows in the window where the customer types the quantity.
It does not appear on the product listings — only on the product page.
If the product has variants, the number follows the selected variant: pick "M", see M's stock.
If it's a combo, the number shows how many combos you can put together, capped by the scarcest component.
Turn it on if you want urgency ("only 2 left") or if you sell wholesale, where the customer needs to know their order fits.
Leave it off if your stock is high (nobody needs to know you have 480 units) or if your stock isn't up to date in the system — a wrong number on screen is worse than no number.
Products without stock control simply don't show the number: there's no quantity to report, so the switch is ignored for them.
"Show a menu with all variations of the products"
Adds a Variations block to the catalogue's side menu, below the categories, listing every variant name in your shop alphabetically.
The customer taps a name and the catalogue shows only products that have that variant. They can pick more than one.
It works when variant names are the same across products. A clothing shop with S, M, L on every item gets a size filter for free.
It works badly when each product uses its own naming ("Size M", "M", "Medium"). The menu then becomes a long, confusing list. If that's your case, standardise the names before turning it on.
The menu lists variants from products that are active and visible in the catalogue. And when filtering, Jarbas only shows products whose variant of that name still has a balance — unless you set out-of-stock products to Show normally.