From what I understand, it’s normally recommended to change coolant every 2-3 years. I’ve stumbled across this “Putoline Ultracool 12” which claims:
The use of powerful corrosion inhibitors means Ultracool 12 is practically unaffected by ageing and can be used for the entire service life of the engine.
Doesn’t the coolant normally pick up some small debris over time, which would still affect cooling? So, even the properties of the coolant itself are largely unaffected, you would still need to flush eventually to get rid of the foreign rubbish in the system.