How to clean and optimize my Mac Storage?

Please review Free up storage space on your Mac - Apple Support and Optimize storage space on your Mac - Apple Support.

Never download or install any non-Apple product claiming the ability to "clean up" or "optimize" your Mac. Those things are all scams.

I agree. one of those cleanup apps will likely only cause problems. Why you need to do is to delete sufficient files or you can add an external disk, copy files onto it and then delete them on your HD to clear the needed space. These days these disks are cost effective, compact, easy to install with vendor provided USB cables and most do not require external power. You may have to reformat it though. There is a large selection of disks to choose from. This solution will allow you to easily have the storage you need.

Preface - It is usually good computer practice to keep between 15% - 20% of the Total Drive Capacity as Free Space at all times.

Allowing the Drive to get below these levels, may lead to a lot of work to get that Empty Space back

Rebuild the Spotlight index on your Mac

What is “Other” storage on a Mac, and how can I clean it out?

Free up storage space on your Mac

OmniDiskSweeper Safe to use

GrandPerspective 

How to delete Time Machine snapshots on your Mac

See used and available storage space on your Mac

Locate backups of your iPhone, iPad, and iPod touch

Notation - If the user is using a cloning software like Carbon Copy Cloner - suggest tweaking the Safety Net Feature in this software. It may be making additional Snap Shots that are not being Cloned to the Eternal Drive. If this should be the case, these Snap Shot could be using additional space on the drive 

The final word from Apple on Managing the " Other/ System Data “ Category

Other / System Data: Contains files that don’t fall into the categories listed here. This category primarily includes files and data used by the system, such as log files, caches, VM files, and other runtime system resources. Also included are temporary files, fonts, app support files, and plug-ins. You can't manage the contents of this category. The contents are managed by macOS, and the category varies in size depending on the current state of your Mac.