Cannot delete images from Messages on Mac (to free up space)

I would try to restart the Mac to see if that solves the issue, but otherwise, you can find all attachments in the following folder:

~/Library/Messages/Attachments

They’re sorted in many folders, but you can use the size of each folder to see which ones contain the files you care about. Bring up View Options in Finder (View > Show View Options) once you’re in the Attachments folder and check “Calculate all sizes”.

Mark Ritter (Author)

Perhaps a path to Learn more about Messages on Mac could be

easier if you look into Messages User Guide for Mac. This guide

has variable content based on the macOS your computer uses.

[Previous versions had Help files within each macOS installed.]

Delete messages and conversations in Messages on Mac - Apple Support (macOS15.x)

//support.apple.com/guide/messages/delete-messages-and-conversations

-icht1035/14.0/mac/15.0

More specific to Messages/Mac, this is one of several User Guides

and these have Table of Contents; easier to find content through

the search item in each TOC access point. [You may also access

other versions of this Messages User Guide for older macOS.]

Shows all versions of this guide:

What’s new in Messages on Mac? - Apple Support

Messages User Guide for Mac - (Table of Contents) Apple Support

.Recent version of Table of Contents (15) in macOS Messages guides.

Adjust version range to see different info ~ example:

Messages User Guide for Mac - Table of Contents - Apple Support

//support.apple.com/guide/messages/toc/14.0

For 'Big Sur' Messages User Guide, see older listed ones or change

macOS version numbers, to reveal guide's table of contents..

Welcome to Messages on Mac User Guide [TOC] - Apple Support

//support.apple.com/guide/messages/toc/12.0

• Mac User Guide (Table of Contents) hardware+software - Apple Support

//support.apple.com/guide/mac-help/toc

All these may be useful or just a bit confusing too. Oh well.

(IF you need more help, visit the Messages Support website.)

I've many bookmarks across few good browsers on vintage

Macs; some run a bit different, in later hardware; if at all.