Trouble saving custom presets

I upgraded to a new MacBook and updated to a newer version of GarageBand, updated my various Arturia packs (October 2025) - everything working fine, but today I wanted to work on some custom presets, and things are not going well.
Briefly: when I create a new preset, or alter an existing one, the “modified” indicator (the asterisk in the box containing the name of the preset) is shown fine. But
(a) when I select “Save preset”, it is not reset, which makes me wonder whether anything is saved
(b) when I select “Save Preset As…”, and select a new name, the asterisk disappears
(c) trying to open a preset I saved earlier shows only the presets I created on my old machine (these were clearly transferred fine), but there is no sign of any newly saved presets
(d) when I try “Save Preset As…” and enter the name of a newly saved (but invisible) preset, I get the error message “You are trying to update an existing preset. Operation not permitted.”

This would seem to suggest that
(a) updating an existing preset (“Save Preset”) is not working. I am not sure where Arturia saves its user presets, and searching for files containing the name of one of my old custom presets does not produce any hits;
(b) saving a new preset does do something, as (i) the altered indicator is reset and more importantly, (ii) trying to save another preset as the same name is prevented because the preset already exists.

My questions: where is Arturia saving my new custom presets, why is it not updating the existing ones, and how can I make the “Save” and “Save As…” operations behave as expected?

Thanks!

K

Update: I have found the folder where Arturia keeps presets, and I discovered that the old presets (the ones I can see in the user preset list from within Augmented Strings, load, and use) are shown as being of kind “Unix Executable File” (but not having a file extension), while the new ones are shown as being of kind “document” (also without file extension).
So: Saving As seems to produce a generic document, which is subsequently (and unsurprisingly) not recognised.
Why would presets not be saved correctly?