1. Feliway Pheromone diffuser Multicat (for households with more than one cat) or original for single cat households:
2. VetriScience Composure treats as a natural supplement to address stress:
OR Royal Canin Calm Feline dry diet instead of the treats:
3. Environmental enrichment: plenty of vertical climbing space, multiple food and water stations, multiple uncovered large clean litter boxes, various toys, cardboard, rope or carpet cat scratchers (whichever your cat prefers). You can read more about these measure here: https://indoorpet.osu.edu/cats/basic-indoor-cat-needs
I would suggest taking these measures for 1 month to see if your cat's hair loss begins to resolve. If not, a trip to the vet would be in order to assess for uncommon causes of unexpected hair loss without skin lesions.