The chest x-ray shows :

There is consolidation involving the left upper lobe with silhouetting of the left cardiac border and air bronchogram.

There is volume loss in the left lung field and juxtaphrenic peak sign on the left.

Juxtaphrenic peak sign is a radiological sign that involves tenting of the medial half of the hemi-diaphragm secondary to upper lobe collapse. It can be seen on right or the left side. Mechanism is supposed to be due to traction by the collapsed upper lobe on the oblique/inferior accessory fissure.

As for above patient, there is collapse consolidation of the left upper lobe likely secondary to an infective etiology given the fever and acute onset of symptoms. Mucus plugging or foreign body obstruction of the left main bronchus needs consideration.

Once patient gets clinically better, a follow up chest x-ray in 6 weeks is a must to ensure resolution of initial x-ray findings.

Further reading https://journals.lww.com/thoracicimaging/Fulltext/2006/03000/Signs_in_Thoracic_Imaging.20.aspx