Oil in liquid form

Good morning, I ride my motorcycle all year long, as long as the weather permits. The problem is, if the Kawa is outside at temperatures below 5°C, the oil becomes so thickly liquid that my E-starter comes to its limits. The pistons move only very tediously in the cylinder and it does not get enough turns to start. even pushing is extremely difficult with 2 men. Once the engine has run a few minutes it also immediately starts again. (oil gets warm and thinner) and runs much easier when pushing. Even in the empty run you notice an increased resistance in the engine. Battery about 1 year old, valves set, carburettors are clean, no false air, oil change about 6 months ago, Choke works, spark plug about 6 months old. Temporary solution is a splasher start pilot, then it ignites once and runs independently. Oil: mineral oil base 10W40 Polo brand Which oils are better (thin liquid) for the Wint He? Is the brand suitable for the Kawa gpz 600 r? At the last oil change the oil was still in good condition (no water or excessive chips) Greeting