There’s no way for someone on thw internet to tell you if your caliper is seized by looking at that picture! You need to turn that piston in order to compress it. So if you’re just trying to compress it without turning it, that’s why it’s stuck.

Yup. New caliper time

This type of caliper needs a special tool to get the piston to retract, these can’t just be pushed back in, they have to be twisted in. If the piston isn’t falling out of the caliper and there isn’t any fluid seeping around the piston then you might be okay, most auto parts stores have the tool you need to twist it back in for rent.

Would like to add that the slot needs to be in the center just like it is now so the bump on your pad has somewhere to go. Make sure your match the pads to the old ones (likely 2 go on piston side and 2 on the other)