Hi @ilyav ,
As far as I know this is not possible, it is a feature that is not supported at the moment.
You can consider pre-setting this theme on Power BI Desktop and then use this theme for report publishing. There is no way to apply the same theme for the entire workspace at this time.
Community Support Team _ Caitlyn
If this post helps then please consider Accept it as the solution to help the other members find it more quickly.