Sure it is, but that's not a way to store value (what economists specifically call store of value if you want to read more about it), which is a little different:

If you buy a €100k rolex, you probably can't be sure you can sell it for more than €100k anywhere at anytime in the future.

You probably can't even find a bank that would take that €100k rolex you just bought as collateral for €500k on a 30y mortgage.

That's why a €1m watch collection is never going to be worth €1m unless we're talking raw materials.