What is the ruling on working in a store where the sale of lawful items predominates over unlawful ones, given that the work is restricted to the store's warehouse and involves no interaction with customers? And is the salary received from the security company contracted with the store considered mixed (halal and haram)?

There is no harm in working as a guard for shops that sell permissible goods. However, it is not permissible to guard places designated for haram (forbidden things) or where haram predominates, such as usurious banks and 술집s, due to Allah's saying: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression." If the store predominantly sells permissible items and does not aid in haram, then there is no harm in continuing to work there, especially if it allows you to perform prayers on time and keep your beard.