You can't add planner to a private channel in teams! Or can you?

Spoiler alert: you can.

Once the planner/tasks group is created, get a link to the planner/tasks and make a website link in the private channel.

Elegant? no
Effective? yes?

Control Private Channel Creation in Microsoft Teams

Well, private channels can get out of hand.
I had some employees make private channels, leave them, and it resulted in orphaned channels that no one could access. Microsoft will probably come out with powershells to take ownership, but as of now, I can't find anything.
So...
Like all admin solutions, I want to take it away.
The hammer approach is to remove employees from team ownership.
But what if you (IT) don't want to manage every teams members? Which is a PITA.
Teams Policies!
In the MS Teams admin center
Teams>Teams Policies
There it is! Create Private channels. I'll just turn that off. I'm an admin, so I should still be able to make private channels.
Turned it off, tested making a private channel, good to go.

BUT WAIT... there's more.

Any O365 change takes 24hours to do anything. In 24 hours I couldn't make private channels either. DOH!

So I can create a new one, but then I'd have to add EVERY PERSON TO THE POLICY...
Or...

What worked for me:
I left the Global policy as follows
Custom policy:no
Discover private teams:Off
Create private channels:Off

Then I created a new policy
Custom:yes
Discover private teams:Off
Create private channels:On

Then I added myself and the other admins to the new policy, 24 long hours later everything is working well.
I can create private channels, and no one else can, unless I say they can. Because I am the admin, and that's how it works.

If you're reading this, I assume you have already completed this step, but if not, here is the document to restrict group creation:
https://docs.microsoft.com/en-us/microsoft-365/admin/create-groups/manage-creation-of-groups?view=o365-worldwide