How can I help a Scottish Fold adjust to a new sofa?

That's a good point about making the sofa feel like theirs. I'd say the best trick is to rub a soft cloth on their favorite sleeping spot or blanket and then wipe that same cloth over the new sofa's cushions - the familiar scent helps them claim it faster. Also, toss a few of their favorite treats or a little catnip on the sofa when they're not looking, so they discover it on their own and associate it with positive vibes.

I've always found that putting an old, well-worn blanket or a piece of your clothing on the new sofa does the trick better than any fancy spray. Cats are creatures of habit, so they need something that smells like home-your scent or their old favorite spot. Just drape it over a corner where they like to nap, and let them discover it at their own pace. No need for all this newfangled nonsense.

Putting a scratching post right next to the sofa is a complete waste of time, honestly, cats will just ignore it and scratch the furniture anyway. Instead, I'd toss a crinkly toy or a cat tunnel on the sofa while they're playing nearby - it distracts them and makes the spot feel like a fun zone rather than a foreign object. But then again, if your Fold is stubborn like mine, they'll probably just sleep on the floor out of spite until they decide the sofa is theirs, so don't stress too much about it.

Placing their bed or a favorite blanket on the new sofa before they even see it helps them claim the spot as their own. Let them approach it on their own terms, without forcing them onto it.

Tricking their sense of territory works better than coaxing or scent-spreading. Instead of forcing the sofa into their world, bring their world to the sofa-place a cardboard box or a paper bag on it for a few days. Scottish Folds are naturally curious about confined spaces, so they'll explore the sofa through the box first, and the unfamiliarity fades fast. Once they're comfortable in the box, remove it and watch them claim the cushions as their own.