Unzip “Jiigetsu Brushes - Clip Studio (beta).zip”, then drag the .sut files onto Clip Studio's Sub Tool palette, or use the Sub Tool palette menu → Import sub tool.
1Unzip the Clip Studio zip.
2In Clip Studio Paint, pick the tool group you want (e.g. Brush) so its Sub Tool palette is showing.
3Drag the .sut files onto the Sub Tool palette, or palette menu → Import sub tool… → select them.
Beta conversions: close to the Procreate originals, not identical.