A lot of people have been asking to use Luminar 4 as a plugin in AF. The plugin doesn't work on MacOS Mojave and newer versions. The reason for this is that MacOS sandboxing blocks AF from writing a temp file for the plugin. When you try to launch Luminar as a filter plugin you can see this in the console logs.
IIOImageWriteSession:115: cannot create: '/tmp/MacPhunPlugin-0x600004050a10-283133786.tiff.sb-04646d08-HWTgPU'
error = 1 (Operation not permitted)
Sandbox: Affinity Photo(88594) deny(1) file-write-create /private/tmp/MacPhunPlugin-0x600004087bf0-292523316.tiff.sb-04646d08-452MfV
Often a way to fix this is to give the app full disk access in the MacOS preferences, however not in this case. I'm not sure why the sandboxing denies the creation of the file. The /private/tmp file _should_ be writeable by default so perhaps it's the function call being used to create the file? Affinity developers I hope this information is helpful and that you can come up with a fix. It would be quite handy to use Luminar as an AF plugin.
