Try extracting the mapping logic into a separate @Component and use @Named, for example, to call the desired method.

@Mapper(componentModel = "spring", uses = ProductMapper.class)
public interface MainMapper {

    @Mapping(source = ".", target = "product", qualifiedByName = "mapProduct")
    Target map(SourceDto dto);
}

@Component
public class ProductSelector {

    private final ProductMapper productMapper;
    private final String desiredId = "curr"; // or inject it from config

    public ProductSelector(ProductMapper productMapper) {
        this.productMapper = productMapper;
    }

    @Named("mapProduct")
    public Product mapProduct(SourceDto dto) {
        return dto.getProducts().stream()
                .filter(p -> desiredId.equals(p.getId()))
                .findFirst()
                .map(productMapper::toProduct)
                .orElse(null); // or throw an exception
    }
}

Alternatively, you can inject ProductMapper via constructor if you rewrite MainMapper as an abstract class:

@Mapper(componentModel = "spring")
public abstract class MainMapper {

    @Autowired
    protected ProductMapper productMapper;

    @Mapping(source = ".", target = "product")
    public Target map(SourceDto dto) {
        ProductDto productDto = dto.getProducts().stream()
            .filter(p -> p.getId().equals("curr"))
            .findFirst()
            .orElseThrow();
        Product product = productMapper.toProduct(productDto);
        Target target = new Target();
        target.setProduct(product);
        return target;
    }
}