The official guidance is to create Project level feeds, unless you know what you're doing. And to discourage users, you need to create a new feed using the REST API instead.

Can No Longer Create Organization-scoped Feeds - Developer Community
Developer Community for Visual Studio Product family

Exactly how, the issue doesn't explain. So let me show you how I did it.

1. Create a Bogus Feed

Navigate to the Artifacts Hub and hit the + Create Feed button. Enter a bogus name for the feed. Don't hit create yet!

Then open the Developer Tools in Chrome or Edge. Go to the Network tab and hit Create to create the feed:

2. Capture the POST call

From the Network tab, find the POST call to the _api/Packaging/Feeds endpoint and copy it as PowerShell (or the kind of scripting language you're familiar with).

3. Change the call to target the Organization level

Change the following elements:

  1. Remove the Project GUID from the POST URL ant the Path header:
  2. Remove the Project element from the payload
  3. Change the temporary-bogus-name to the desired value
  4. Add -UseBasicParsing if, like me, you don't have Internet Explorer installed
Don't copy my values verbatim. The Identity Descriptors are specific to you account and you need a valid Bearer Token.

Now run the code and: there's your feed!

Note: this example doesn't change the authentication headers, the Bearer Token will expire, breaking the code. You can replace then Bearer Token with a base64 encoded PAT string.