I have to leave my accommodation at 12 noon but my flight is not until 8pm.
Is there any place to leave my luggage in Granada?

The most comprehensive information about left luggage locker in Granada is here
https://infoaboutspain.com/idx.php/17/039/article/Where-can-I-leave-my-luggage-in-Granada-.html

This is a copy

Where can I leave my luggage in Granada?
Left-luggage lockers in Granada:

Granada City Center Luggage Storage:
Very convenient place near the cathedral. Leave your bags for hours or days.
There are discounts for advanced booking
Click here
https://www.mireservaonline.es/en/services/granada-city-center-luggage-storage.aspx?p=ojmilhjjommioqnjjpjjinipsqjkjiql


Ilocker:
There is a left luggage place in Plaza Nueva
https://www.granadamap.com/ilocker/index.htm

Bus station
There are lockers at Granada bus station.
https://granadamap.com/placemap.php?place_id=59

To get to the bus station get on a 33 bus from the Gran Via and Avenida de la Constitución

Alhambra
Also there are lockers at the Alhambra. It is free if you have bought a ticket. The luggage office is located outside and downstairs from the main ticket office..

There is some more information here
https://granadainfo.com/alhambra/lockers.htm

We Locker Granada
Just behind burger king in Puerta Real
Calle Campo Verde, 2, 18001 Granada
622 61 00 06
https://welocker.es/?lang=en
This website appears to be down maybe they don't exist anymore.

Lock and Be Free
Address: Salamanca, 13
This is a side street between Plaza del Carmen abd Bib Rambla.
The website is not very up to date with info about the Granada office.
https://lockandbefree.com/book-salamanca-str-13-granada