Certified GKH Gardening Expert
This begonia appears to be suffering from a bit of environmental stress, most likely a combination of low humidity and direct moisture on the leaves during light exposure. The browned, crispy edges and blotchy tan sections are typical signs of minor leaf scorch or dry-out, especially common in rex types with delicate, fuzzy foliage. It doesn’t look like a pest issue—there’s no webbing, stippling, or mold—just some localized tissue damage from inconsistent watering or exposure to sunlight after misting. Going forward, it’s best to water at the base with rainwater or distilled when possible, keep the soil lightly moist (not soggy), and boost humidity around the plant with a tray of pebbles and water nearby. You can trim the affected edges with clean scissors, and the plant should bounce back just fine. Avoid misting the leaves in direct light and ease off on any fertilizers for now. This one’s an easy save.
I'd recommend keeping an eye on soil parameters, as well:
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/testing-soil.htm
This collection will offer more information on begonias:
