Thanks for the clear explanation solutions.
Note for Affinity Devs:
So since this creates unexpected results for the users, and I don't see ever anyone wanted to get this results purposely, why not program it so the Artboard would always position themselves at whole pixels, no matter what the design settings are? This should be the default behaviour. If you really want the Artboard behave like this, part pixel, then just make it a separate setting, but not by default - and add a clear warning about this outcome on exports.
On the other hand of the argument, here are results of unexpected behaviour:
A - designer hands over artwork to client, not noticing the thin border, most likely. Client will later try to incorporate it in other designs, websites and gets this weird thin border around. Not a happy client, not great for designer.
B - less often than A, designer notices issue after export, but only if there is a need to incorporate that in a a design, it's not noticeable otherwise. As a results, need to spend time figuring what is wrong and re-exporting. Unhappy Designer.
So what is the counterargument for that behaviour that would make this an acceptable outcome? I understand having the design tools setting for whole or part pixel, but not the artwork itself. If you think that anyone would require this half pixels for artboards, then just add that option on the settings, instead of having it behave like that by default. Again, I do not see why would anyone require that for artboards.
Cheers!