Currently, there when viewing the burnup report in a next-gen project, there is no way to eliminate non-working days, such as weekends or holidays. This is something you can do in classic projects by configuring the board -> Working days and selecting which days of the week your team typically works.
Ability to configure working days in a next-gen project
The burnup report is less helpful for any sprint/project that runs multiple weeks in the current setup. Having 2/7 days a week where teams are commonly not working is skewing the effectiveness of this report in regards to how team leads/management estimate time it takes to complete tasks.
Also this is functionality that exists in Classic projects