When using About this Mac >> Storage, what does the category "Other" mean

Manage Storage

It is generally a good computer practice to alway keep at least 15% to 20% of the Total Drive Capacity’s as Empty Space. Allowing the computer to drop below these guidelines may eventually, cause unintended consequences.

The links below will assist in identifying what is taking up space on the Internal Drive and provide possible ways to remove data that is under the direct control of the User ( Home Folder ) . 

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.

Welcome but head scratching here regarding " Looks as though I need an upgrade " ?

Reading between the line ( guessing ) a new computer with a larger Drive Capacity ?

If the user wishes to explore the Apple Trade-In  Process where the Value of the exiting device could be used against the cost of a new Apple Computer, iPhone or iPad  

Or Shop Refurbished Apple computers at an Apple Reduced Cost

Just be sure to purchase a machine with a Drive Capacity and RAM big enough for what you anticipate your needs will be in say 2 - 3 year looking forwards from Now

Have used both previously and have been satisfied each time.

See the Other category in this article: See used and available storage space on your Mac – Apple Support (UK)