Mark:
Thanks for your quick reply. (BTW: Were you at Superbooth '22 at the Percussa SSP booth?)
I’ve answered your email below by embedding my replies in bold to your questions.
on macOS:
I’m assuming you have already upgraded to the latest image using belenaEtcher? ==> correct, created using belenaEtcher with the Superbooth '22 image from the forum website
you are then seeing the BOOT (fat32) partition on your desktop? ==> correct, macOS Disk Utility reports USB External Physical Volume - MS-DOS (FAT32)
Im assuming you used the sdcard that came with the SSP… and that its has enough capacity. ==> both supplied microSD card AND my own SanDisk 32GB microSD card with the latest image on it
but the issue you are having is you cannot copy things to the samples/plugins directory? ==> macOS Disk Utility reports that the Mount Point (Read-Only): /Volumes/BOOT
SSP boots, runs factory patches? you are on latest image? ==> correct, SSP boots without any issues, runs all factory patches using the latest image (see reply above)
(have you just upgraded? so this is a new ‘image’) ==> correct, see previous reply
lets now checks some things…
if you are using an sd card to micro sd card adapter, check it doesn’t have the ‘read only’ tab slide across to read. ==> I was hoping that was the issue; unfortunately, no, the read-only tab is write-enabled
k, lets take a closer look at the sd card,
launch disk utility, then click on External/BOOT , (take extra care do make sure you DO THIS) ==> on my system, Disk Utility indicates just “BOOT”, no “External” (see screenshot below)
at the top it should say MS-DOS(FAT32) ==> correct, macOS Disk Utility reports MS-DOS (FAT32) for the BOOT partition on device disk6s6
not click on First Aid, and it’ll check the drive for errors ==> was this a typo? did you mean that I should click on Disk First Aid?

one reason filesystems can be marked ‘read-only’ is if the OS thinks that are damaged…
(though, this tends not to happen on fat partitions)
on macOS, it’ll silently ignore partitions that it cannot mount. (in this case the ext3) and mount those it can (fat32)
as for windows 7 ‘issue’ , things are different…
on Windows, it will mount the partitions it recognises (fat32) and whinge about ones it cannt (ext3).
this is ok, we only need to mount the fat32/boot partition to transfer samples/plugins etc.
overall its quite difficult from here to know whats going on…
basically the ssp image you have written with belenaEtcher to the sdcard is ‘complete’ ==> belenaEtcher reported that the disk image was created successfully without errors
so contains multiple partitions, including the FAT32 one that contains the default factory presets etc, and should be writeable on all operating systems. ==> correct
no extra steps are needed, its should “just work” ™
we could jump to conclusions, about the write failing, or dodgy sdcard - but honestly, we don’t really have enough information. esp. as things like belenaEtcher do verify the write process, so you’d expect that to fail, if its bad.
similarly, if its was a bad write/image - there are checksums to verify against, and also you’d not expect the SSP to even boot.
so, whilst you could try another sdcard if you have one (why not
) , its all a bit odd still. ==> I have two microSD cards, one supplied by Percussa with an old OS, and a new SanDisk 32GB card with the latest image, both boot successfully on the SSP
(*) none of this is a special ‘percussa’ thing either - this is a standard workflow, that 1000s/millions of devs do all the time for developing on other systems, e.g. raspberry pis, so it’s very reliable.
Ive never personally seen it fail, and I do it a lot 
however, I will say I always use high quality branded sdcards … this is NOT an area to save money on. cheap cards fail more often, and usually don’t give you the performance that they claim on the packaging… don’t believe those telling you otherwise, you get what you pay for! ==> I’m using the same brand microSD card as supplied by Percussa SSP, SanDisk, and the same capacity.
Also, in Terminal, the permissions on the BOOT partition show as:
drwxrwxrwx@ 1 admin staff 16384 Aug 6 12:16 BOOT
Regards,
John