Shopify builds three themes of its own, and they behave differently with motion. Here is what each one does on its own, and what happens when Segue is switched on.
Dawn
Dawn is the reference theme: fast, plain, and the base of hundreds of others. It has no page transitions and no preloader, by design. It supports app embeds like every Online Store 2.0 theme, so Segue switches on in the theme editor and reads Dawn’s colours straight from its settings: the button colour, the link colour and the colour variables Dawn defines on the page. Your logo comes from the brand settings. Every one of the fourteen styles has been run on Dawn, and Lighthouse shows no drop.
Horizon
Horizon is the first Shopify theme with transitions of its own, built on the browser’s view transitions: pages cross-fade and a product photo flies from the card into its page. They are good, and they are one look. With Segue on, Segue takes over the navigation so the two never fight; Horizon’s own transition steps aside for the move you chose. If you want the product photo to keep flying, Automatic mode does that: a product photo flies into its page, a button grows, and everything else gets Wave.
Horizon also sets a few rules of its own that an app has to respect, such as naming the same photo box for its own flight; Segue works around them, which is one reason it is tested on Horizon with every release.
Pitch
Pitch is Shopify’s editorial theme, with big type and a product gallery that is laid out differently from Dawn’s. All fourteen styles pass on it; one fix was needed in Segue, not in Pitch, for the way its gallery frames the product photo. Pitch has no transitions of its own, so there is nothing to switch off.
Every other theme in the Theme Store
Every theme in the Theme Store is Online Store 2.0 and supports app embeds, which is all Segue needs. It does not matter whether the theme was built by Shopify or by a studio, and theme updates never touch it, because nothing of Segue lives in the theme’s files. If a third-party theme ships transitions of its own, switch one of the two off; running both is a fight neither wins.
Headless and Hydrogen
Segue is an app embed for Online Store themes. A headless storefront on Hydrogen has no theme editor and no app embeds; its transitions are written by its developers, which is a different conversation. If that is you, write to the studio; the studio builds bespoke motion as well.
In short
Dawn: nothing of its own, everything from Segue. Horizon: its own transitions, which Segue takes over. Pitch: nothing of its own, every style passes. Any other theme: the same three clicks in the theme editor, no code.