Currently, we're unable to customize the open bill reminders like to show specific vendors or amounts. I'll take this as feedback and submit this to our product engineers. Please know that the implementation of this feature will be based on the number of customers requesting it.
In the meantime, you can visit our blog site to stay current with our features and product enhancements.
To know more about running reports of open bills, you can refer to this article: Enter and pay bills.