Pretty sure they use a belt. Regardless of the low mileage and to be on the safe side, after 21 years I’d make it my first job to change it if it’s not been changed in say, the last 7 or 8 years.
Just had a look on Autodata here......if your Picanto has a G4HG engine (2004-2005) then it does have a belt, with change intervals at 60k miles or 6 years.
Similarly if it has the Hyundai G4HC, G4HD engine (1998 - 2005) then it's the same, near enough.
You can tell because the belt has plastic covers on the engine offside. It's not particularly stressed and easy enough to change, but do have it done, complete with the tensioner.
Other than that, study MOT history where you can, look for corrosion and crash damage, emulsified oil under the oil filler cap and so on.
John
Soapy oil on the dipstick or inside the filler, I had that on mine about that age and I am sure the head gasket was on it's way.
Another was the engine check light coming & going randomly, I think the wiring starts to get corroded at the connectors, never did find the fault!