Is your garage attached to the house?

No garage. when you sink the pots (in the garden soil?) do you cover them?

Greenhouse, but before I had one, I used to use home-made cold-frames. Basically, I wanted to store the seedlings in one place, where I could keep an eye on them, while protecting them from rain, pests and the usual problems which can beset our treasured, but fragile baby plants.

Yes, to covering, I like to keep young plants fairly dry over winter as it is often the wet, rather than cold, which will do for them. A coldframe is mostly to keep out birds and rodents - the temperature is not much different to being outside but, in a prolonged freeze, it is easier to minimally heat a small frame with christmas lights.

Do you have space next to the foundation where you can sink the pots? The roots will stay warmer in a January cold snap if they are close to the house.

What does sinking the pots do versus planting the cuttings directly in the ground?

Nothing really, apart from providing some shelter (from thermal mass/house walls). As a temporary holding space, being closer to the walls will raise the temperature slightly, and you can then lift and transplant the seedlings in their permanent spots in the open garden, after the winter weather.

Roots won’t be disturbed when you sink the pots

Would under a covered porch work, or not enough llight?