Image icon has changed to upload icon

My users notice that the add-an-image icon in the toolbar of the message compose window is no longer an image but is now an upload. This is on desktop, and only image uploads are allowed, as is the default.

Maybe this is a regression? I see these previous similar reports which were accepted and fixed:
Upload Icon should be Image Icon
Image button icon instead of upload icon

(I’ve tried removing heic and heif from the allowed formats but that’s made no difference, so I suppose the root cause is different this time.)

(I don’t have a ‘secure media’ setup)

FYI this is caused by the webp extension, if you remove this it goes back to an image icon, just to help the team troubleshoot.