> how common it is for super market to use obsolete software (especially for the part which carry some security risk like something with remote control).

It's a near guarantee. I've been in dozens of power plants where the engineering workstations or operator interface terminals are running Windows XP or Windows 7. More than zero of which were not properly air-gapped. If those sites (with sizable CapEx budgets) delay upgrading for various reasons I would expect grocery store chains to keep whatever they have running until it's broken to the point of not being fixable without a complete overhaul.