This is because you don't have UIMaterialLab in your content folder. You need to download it from the Epic games Store in marketplace section. or by using this link www.unrealengine.com/marketplace/en-US/product/ui-material-lab You can either create a new project based on UIMaterialLab and create this radial progress bar there, or you can put UIMaterialLab folder to your project.
Thank you
But i cant find MF_UI_polarcoordinates
This is because you don't have UIMaterialLab in your content folder.
You need to download it from the Epic games Store in marketplace section. or by using this link www.unrealengine.com/marketplace/en-US/product/ui-material-lab
You can either create a new project based on UIMaterialLab and create this radial progress bar there, or you can put UIMaterialLab folder to your project.