A change log for this major v6.0 release is available at https://www.ccleaner.com/ccleaner/version-history.
Information about the new Performance Optimizer in v6.0.9727 can be found at Our CCleaner 6 App is Out Now With a New, Patented Performance Optimizer and Improved Software Updater. Recall that NortonLifeLock acquired Avira in 2020 and then acquired Avast (including its subsidiary Piriform, the original creators of CCleaner) in 2021, so I expect we'll see more of these "system optimizers" and other bloatware developed by Avira and Avast continue to creep into both CCleaner and NortonLifeLock products in the future.
I still like the Custom Clean function of CCleaner for disk cleaning and use the Portable (zipped) version to avoid having to install all the unnecessary bloat on my system, but if you try to download CCleaner Portable from the builds page at https://www.ccleaner.com/ccleaner/builds you are currently offered the previous ccsetup592.zip file. According to nukecad's 13-May-2022 post in CCleaner 6.0.9727 Portable Not Available the programming changes in v6.0 caused "a few issues" and a Portable version of CCleaner v6.x likely won't be posted on the official builds page until v6.1 is released next month.
I have a 64-bit OS and use the default English interface, and when I unzip the Portable ccsetupxxx.zip file on a removable USB thumb drive there are only three essential files I need to keep - CCleaner64.exe and portable.dat plus my "old" ccleaner.ini file (which stores the custom configuration settings I made in my previous CCleaner Portable versions). Hopefully that won't change when CCleaner Portable v6.1 is released next month.
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Dell Inspiron 5584 * 64-bit Win 10 Pro v21H2 build 19044.1706 * Firefox v100.0.0 * Microsoft Defender v4.18.2203.5-1.1.19200.5 * Malwarebytes Premium v4.5.9.198-1.0.1676 * Macrium Reflect Free v8.0.6758 * CCleaner Free Portable v5.92.9652