This is a known issue with the Tesla Model Y, other Tesla vehicles. This is noted in the Tesla Model Y Owner's Manual - Parking Brake.
Warning! - In snowy or icy conditions the rear wheels may not have sufficient traction to prevent Model Y from sliding down a slope, particularly if not using winter tires. Avoid parking on hills in snowy or icy conditions. You are always responsible for parking safely.
Model Y Owner's Manual | Tesla
Never park the Tesla on a sloped driveway or parking space that is covered in snow or ice. The Tesla vehicle is only held by the rear brakes when parked, the front wheels are not locked by a transmission as with ICE vehicles with an automatic transmission. (Think of the Tesla vehicle as if it was a heavy RWD vehicle with with a manual transmission.) Only the parking brake prevents the rear wheels from moving, there is nothing locking the front wheels. On snow or ice the rear tires can easily break free and slide, the front tires will start to roll.
The driveway or parking space must be clear of snow and ice. Apply cat litter or other abrasives to the driveway to improve traction. There are Youtube videos that show the Tesla Model 3 sliding shortly after being parked.
If you have to park on the street be sure to point the Tesla vehicle down hill if possible with the front wheels angled towards the curb. (If you must park facing up hill then angle the front wheels away from the curb.) When possible position the Tesla vehicle so that the front tire contacts the curb.
