No, it’s not ok to leave a solar deck light out in winter unless specified on the label. Generally, solar-powered products don’t do well in extreme temperatures. They need mild conditions to convert solar energy into light energy (5).
Think of it like running a power cord from your house to your shed in the middle of winter. You need insulation to keep the wires inside from freezing. But unlike this situation, you can’t insulate solar deck lights. Best to keep them running under the ideal temperatures indicated on the label to be safe.