Updated July 20, 2022:
We’re resuming the rollout of this change in Current Channel. Based on our review of customer feedback, we’ve made updates to both our end user and our IT admin documentation...
Updated Jul 20, 2022
Version 9.0
Blog Post
PhoebeYuan The files will work, i.e. macros can be enabled, by applying one or more of the documented solutions.
tpg017 I don't think the workflow is all that complicated - you may be over-complicating it by thinking you have to do BOTH ticking the Unblock checkbox AND moving it to a trusted location - you don't... one or the other will suffice. But yes, saving the attachment is required first.
And there absolutely is a possibility for admins/users to define trusted sources - that's precisely what trusted publishers are for.
If you mean trusted sources as in the email addresses from which you will trust any macro-enabled files received as attachments... given the possibility of spoofing a sender's email address, I would suggest that is an extremely risky way to handle macro security. Perhaps better would be to ask people who might email you macro-enabled files to use self-certification to digitally sign their VBA projects, then you can add them as a trusted publisher on the receiving machine.