My guess is dirt in the joint is the cause of your squeak. I’m assuming your bushings are either rubber or polyurethane. You could lube the bushings with vegetable based or silicone based grease but I suspect soapy water would also provide some relief. Using oil based lubricant on rubber or plastic parts is bad. The oil degrades the elastomer.
And its not ...
More information on your car would be helpful. Such as mileage.
Here are the places which are a high probability for the clunk you describe:
strut bearing/bushing area looseness and wear
sway bar bushing (I don't know if the Polo has a sway bar)
bushings on control arm
linkages, such as sway bar linkages
The noise is not likely a loose brake caliper, but ...