Doesn't look very hopeful, I'm afraid. But I wouldn't throw t out yet. I'd put it in an out of the way corner somewhere and forget it. Who knows, it might surprise you in a few months.

Maybe cut off all the dead and lightly feed with some miracle grow or similar.. at this point you don't have a lot to lose but you may be pleasantly surprised!

Growing in pots is difficult in our zone for most plants both due to spring and fall freeze-thaw cycles as the weather changes and because months of having the roots frozen solid is hard on most plants since there isn’t the insulation of the surrounding soil mass topped with a blanket of snow that in ground plantings have. I agree with floral that it is likely not alive, but set it aside and keep it watered but not soggy, and see what happens.

if you decide you want to try again with a clematis in that spot, you have a couple of options. You can bury the entire pot up to the rim in a bare area of the garden for the winter. I put them in the veggie garden after our first frost in autumn when I rip out the tomatoes. When they start growing in spring, I pull out the pot, and if need be remove the clematis and refresh the soil. Or you can plant around the corner in the ground and then wrap your support around the corner to where you want to see them. It may take some time and patience training it for the first couple of years, and then after they reach around the corner, only prune back some (instead of back to 3 or so buds per stem as one normally does with a hard prune clematis like Jackmanii) to leave some vines wrapped around the corner so that you don’t need to guide them all every year.

if you decide to go with Jackmanii again, you will want to buy a larger trellis as it can get to 10’ in a single season even when hard pruned in spring.