Dealing with a Pug's Separation Anxiety

Hi everyone, I've noticed that my 5-year-old Pug, Max, seems to get anxious whenever I leave the house. He starts whining and pacing around, and I'm worried about how stressed he might be feeling. I've tried leaving him with toys and treats, but it doesn't seem to help much. Any advice on how to help alleviate his separation anxiety? Thank you!