Reduce the retention and max project versions kept to help reduce the SSISDB size. Check the settings

reduce_ssisdb.sql

-- Make a note of the before
-- Tempted to add into to preserve the before
select * from catalog.catalog_properties

-- Change the settings
exec catalog.configure_catalog retention_window, 30
exec catalog.configure_catalog max_project_versions, 2

-- Check the settings have stuck
select * from catalog.catalog_properties

-- Run the cleanup
exec internal.cleanup_server_retention_window

Ref - https://www.mssqltips.com/sqlservertip/3307/managing-the-size-of-the-sql-server-ssis-catalog-database/