In reference to locations, something is isolated if it is far away, or difficult to access. He lives in an isolated cottage on the moors. The only remaining population is on an isolated island in the Pacific. Secluded means hidden, tucked away. They met in a secluded garden. We also talk about living in seclusion - hidden away from other people. The two terms are certainly not synonymous. Something can be isolated, but not in the least secluded, and vice versa.

A big upvote for Hilary Metcalf's answer. These words have different meanings. As Hilary says, "Something can be isolated, but not in the least secluded, and vice versa." "Isolated" means "like an island" - in other words, on its own. If a person is isolated, they are ( or feel ) that they are cut off from other people. If a place is isolated, it means that it is located far from other places. A single farmhouse standing alone on desolate moorland or bare mountainside can be described as isolated. This means that it is the only building for miles around. However, it is by no means hidden or secluded. In fact, it is the opposite - as it is the only building, you can see it very easily. When you look at the landscape, an isolated building will stand out very obviously. If something is secluded, it means that it is hidden or private. Imagine a millionaire's mansion in a built-up suburb where there are lots of other similar mansions. If that house is in the middle of a garden, surrounded by a thick curtain of trees, and hidden from the gaze of photographers and journalists, you can describe it as secluded. But if it is surrounded by other similar properties, and close to the infrastructure of the city, it certainly isn't isolated.

"Isolated means "in a location far away from anything else"; secluded means "hidden." In practice they often amount to the same thing." The cottage is very isolated from the city. The cottage is very secluded from the city. Source: https://forum.wordreference.com/threads/isolated-secluded.1975703/