This is sadly common for kids with ADHD. When my son was little we would be required to invite the whole class but not one of them ever showed up. Fortunately, he had one friend outside of school (with awkwardness of his own) I could depend on to show up, as well as 1 cousin. It went that way for several years.
Once he hit middle school, we started having him invite one friend to the local arcade/go-cart track to celebrate his birthday. We couldn’t afford to invite a group of kids to do that, and inviting only one meant he could choose someone he knew would want to go there, and I could work with that child’s parent to schedule it on a day that worked for them. This worked much, much better!
Invite family, or friends’ kids, or any kids you can think of to make sure someone is there for the party.
ADDitude Community Moderator, Author & Trainer on Parenting ADHD, Mom to teen w/ ADHD, LDs, and autism