germany
Any company property the employee had in their possession is still company property. This is no different for laptops, cars or trucks.
The former employee owes the former employer a way to recover their property (§ 667 BGB). Normally, that is arranging pickup at the employee's home for a laptop, but being available for someone from the employer to pick up any movable goods (keys, papers) that are needed and telling them the location of their property if publicly accessible is enough. This assumes the property was left there for a good reason, not moved away out of spite.
Reasonable accommodations have to be made: you don't have to be available at weird hours for pickup, but telling someone the location of a truck can easily be a phone call or email, so compared to actual physical pickup one has to plan and arrange, there is no reason not to tell the former employer immediately.
It might even be a legal nightmare to actually drive the truck after officially being fired. So parking it at the nearest legal spot after being fired effectively immediate is the only appropriate action here.
If the company had wanted the truck returned, they should have fired the worker after they returned the truck or fired them with a notice period big enough that they can return the truck. "Your last day is Friday, please used the remaining days to return the truck to the logistics center in Citytown" would have been perfectly fine.
Please note that this is not a realistic scenario in Germany either way, because terminating an employee requires the notice to be in writing, just like the original contract. You cannot legally fire someone over the phone or via email. With all the EU regulations on digital signatures on contracts that might change for email, but phone does not produce a paper trail and will not be legally valid any time soon.