What I learned as a glass collector and glassblower is that if you use an item made from a fragile material, it will eventually get broken. The only way to keep such things forever is to put them on a shelf and not use them. If you want to experience it, you must accept that eventually it will be damaged or destroyed.
you can use an indoor adhesive to fill the chipped area, paint it, and glaze it to fix it. there's different adhesives and glazes out there so I would recommend looking into what the mug's made of and trying to match materials. Keep in mind that if it's dishwasher/microwave safe the adhesive/glaze you use might affect that
You can also use a polymer clay and glaze to fix it. Keep in mind polymer clay needs to bake to set so the mug HAS to be dishwasher safe (since it'll be able to withstand high heats!)
Joking aside that's good advice and very informative. Thank you. I am not the one who originally made this btw but I'll use this advice if it applies to me in the future.