If you are using Eclipse and prefer the plugin approach, the update sites archive for version 6.6.0.final may be available on SourceForge. The feature group ID is com.jaspersoft.studio.feature.feature.group 6.6.0.final .

Searching for Jaspersoft Studio 6.6.0? This version, released around May 2018, was a notable update that introduced features like PDF/SVG import and support for the JasperReports Library 6.6.0