So here is what I have understood based on my experimentations.
Notarisation is done to avoid getting the file getting quaratined(which is just a file attribute) when the file is downloaded from the internet.
So if a file is not notarised it is quarantined when you download it and then all sorts of issues popup with the Gatekeeper.
InDesign plugins don't need to be signed per se(I have not been able to test it to be totally sure). Since the normal mode of transferring the file from one machine to another is via the network/browser download it gets quarantined if not notarised.
If you use something like curl to transfer the plugin from one machine to another, you should be able to run your unsigned plugin as well. Although I have not tried this due to limited availiblity of no. of MAC's to me.
Notarisation can only be done on a signed entity
So now you sign the plugin, but notarisation can't be done on folder it can only be done on pkg, dmg or zip's. So in turn you create one of these. Barring zip you again will have to sign it before notarisation and for that you use a different signing certificate.
So the crux is everything inside the pkg, dmg, zip needs to be signed. Then the pkg, dmg needs to be signed and then they are notarised to bypass the Gatekeeper check.
Signing is needed because notarisation can't proceed without it.
If you want to avoid all this rigmarole of signing/notarisation avoid using browsers to download your installers/plugins and you should be good.
I hope this makes sense. These are my personal observations/inferences, I may be wrong on some points and am all ears to someone who wants to share their story.
P.S.:- I also concur that Adobe documentation would have been more helpful if they added some more explanation or context to it.
P.P.S:- Don't try too much time understanding whether this is needed or not, because I am quite sure Apple will sooner or later make it increasingly difficult to bypass this. So it's better to sign/notarise it and get it over with
I'm curious if you received an answer that satisfies your question. I'm running into similar confusion as to what exact steps are needed to notarize and sign multiple plug-ins that get zip'd for transfer to a customer. I've built and signed on one Mac and can use them on that Mac since they were signed using it. But when I copy them to another Mac through an internal connection, whether as plug-in or as a zip'd file containing the plug-in it complains that they aren't valid. While I've worked with InDesign plug-ins for quite a while it has primarily been using PCs and not as versed in necessary steps to do proper natorizing and signing for M1 Mac development using Xcode or command line functions. I've read the document you referenced but as you stated, "seems to be confusingly worded" and the things I've tried have not been successful.
I'm hoping you or someone else can offer a clearer step-by-step process of how to notarize and code sign plug-ins directly and/or the zip file in which they are placed for Macs in order to avoid being flagged for quarantine.
Did you read my post above? That should clear out some confusion for you, if not then list specifically what aspects are unclear/confusing to you I will see if I know the answers to it else someone else would possibly chime in.
Now regarding the steps to use, I follow the following steps and it has not troubled me so far.
Avoid using zip as the format to ship the plugins because you can't staple the notarization ticket on a zip file and if the destination computer does not have access to internet then things could go sideways.
Better is to use a dmg file instead of zip and dmg can be stapled. Use command hdutil
Codesign your plugin during build in XCode, using the Developer ID Application Certificate.
Create dmg as stated above, sample command would be
hdiutil create -srcFolder source MyPlugin.dmg
Codesign the dmg, using the Developer ID Application Certificate. Sample command below
codesign --sign "Developer ID Application: <you full id>" --timestamp ./MyPlugin.dmg