The "Other" section

It is supposed to and it will fluctuate. It appears that one of the "culprits" may be snapshots which Time Machine makes if it isn't hooked up - supposed to clear that out once it is plugged in and caught up.

Personally, I think it is confusing at best, but there isn't a thing we can do about it. You can submit feedback - that may help:

www.apple.com/feedback

You cannot manage that category - see this Apple article:

https://support.apple.com/en-gb/guide/system-information/syspf9b375b9/11.0/mac/11.0

As the Learned Contributor @babowa has pointed out the Other Category is part of the OS can can not be just removed or managed like personal files.

I am hesitant to overload you with such detailed information but here it is.

The Other Category should not be altered, modified, move or deleted nor should it be attempted to be. Doing so may corrupt the OS and rendered the OS inoperative requiring a Wipe and Re-Installation.

The Other category is a potpourri of files which include:

• System temporary files

• macOS system folders

• Archives and disk images (.zip, .iso, etc. - often found in the Downloads folder)

• Personal user data

• Files from the user’s library (Application Support, iCloud files, screensavers, etc.)

• Cache files

• Fonts, plugins, extensions

• Other files that are not recognized by a Spotlight search

• Media files that cannot be classified by Spotlight as a media file because they are located inside of a package

They can be located anywhere on your hard drive. The files that you have control over are located in the Documents, Downloads, Pictures, Music and Movies folders.  You can use either of these two free apps, GrandPerspective  or OmniDiscSweeper, to find the largest files on your drive so you can determine if they can be deleted or moved to an external HD for storage.  

Nothing to be worried about as per your provided number. As long as you keep at least 12 - 15 GB Free Space at all times, you should be fine.