My WordPress is not generating thumbnails – or maybe it is… ?

I am seeing it create:

• the uploaded original, as added.
• a -scaled.ext file.
• one other smaller-scale size, image-name-1568xNNNN.jpeg…

I note that the 1568 is found within the Twenty Twenty One Theme’s functions.php, as set_post_thumbnail_size( 1568, 9999 ); This size is only created when Twenty Twenty One Theme is active.

When Twenty Twenty Three is active, it is not created, only -scaled.ext is.

Shouldn’y I be expecting more, including the 150×150 thumbnail size?

It’s like these Media Settings are being ignored and sizing-down only happens if set in code.

A few months ago, I did go through a big process of media slim-down due to excess numbers of these alt-sizes images, and took steps to stop it happening, including setting the medium and large size dimensions to 0. But now I need to check that this process can actually work…

• I have disabled many media-related plugins.
• I don’t believe I have any code anywhere unsetting size creation.
• The problem is despite sizes being set in Media Settings.

I am running this on MAMP locally, which says GD2 is installed. This often appears as a cause.

It’s not generating any more than the -scaled.ext and one other for both new images and any images on which I run Regenerate Thumbnails (which is currently disabled).