First of all if you are interested in Spanish and Christmas there is a list of vocabulary here which may help you to understand some of the things going on in Spain at this time of year. https://lingolex.com/christmas.htm
Unfortunately the 24th of December is possibly the worst night of the whole year for going to a Spanish restaurant. Spanish people eat together with their family on the evening of the 24th Dec. Therefore almost all restaurants are closed.
You may find some Morrocan restaurants open but even they may close. Here is a Morrocan (they don't serve alcohol here) https://granadainfo.com/arrayanes/index.htm
Chinese restaurants are probably open. A good chinese restaurant is the Leones https://granadamap.com/leones_chino/
Make sure that you have bought enough food so that if you can't find anything open at least you can eat. Everything will be very quiet in the street between about 8pm and 12 pm on the 24th.
The 25th is different you will find most restaurants open.
To be really Spanish have a look at some of the Belens (bethlehem scenes)
Try some Spanish sweets such as polvorones mantecados and turron
If you click here it will show you all places within 1000 metres of Mirador de San Nicolas https://granadainfo.com/nicolas/nearest_places.php
Click on the links to see the most popular activities that you can do in these places:
Note that the booking system uses a Spanish system and there is no involvement of any American company and no US tariffs.