The idea is to have the car on a level surface. Have the jack on solid smooth surface so the wheels can move.
As the jack arm goes up. The distance from the saddle to the wheels changes horizontally. Either the jack moves toward the front wheels or the car has to roll backwards.
When I have chocks for the front wheels. I usually leave 6 inches of clearance between the back of the tire and the chock. So the front wheels will roll back to the chock as the jack comes up.
I don't know where you jack a boxer up. If there is a jack point center rear or if you jack from the sides. Never had one in the shop..
You may want to check the brand of your jackstands. Some harbor freight jackstands were recalled. There is a thread from yesterday here. I even have a set I used. And just positioning them they fell. https://i.imgur.Com/8s7opx1.jpg
but I had to have the height to get the front up