Variation listings are not supported on the app; use the website.
Variations are not supported on auction format listings; use fixed price format.
Make sure you're creating a new listing and not using relist or sell similar from a listing without variations.
Variations are not supported on the simplified listing tool. If you're on the simplified tool you'll see a button on the top right that says "switch to business listing tool" - click on that.
By default the variation setting is hidden on the listing form. Once you unhide the setting it will stick for future listings. On the top right of the business listing tool, click the menu (3 vertical dots), select settings, and toggle the variations slider on (so it's blue).
Beyond that it comes down to category; not every category supports variations.
If the category supports variations you'll find them in a non-intuitive, awkward placement on the listing form - below item specifics instead of above them. I recommend filling out variations before you enter any item specifics or other listing details to avoid problems.
