How can we give permission to post new blog without giving permission to edit already published blog

[vrashi]

I'm working on a blogging platform and we have created a workflow so that whenever someone wants to post a new blog, he has to submit it for approval.
I'm faced with a permission issue. I don't want the user to be able to edit already published blogs but if I remove that permission he looses the ability to add a new item on the platform (so he can't submit new blog for approval).
Is there anyway this problem can be rectified?

[#2]

@vrashi 

How familiar are you with the SharePoint permission model?  There are explicit permissions for both the NEW and EDIT actions you mention.  If you check the screenshot below you can see these.

I've had a look at the SharePoint Online blog site.  Blog posts are posted to a library called "Posts" which do allow you to edit the permissions.  You'd be able to create a new permission group that, by stripping away the Edit Permissions will allow users to add new items but not edit current ones.

If you're NOT using the SharePoint blog subsite template, can you share a little more information on this and your Power Automate workflow.  Manipulating item level permissions within Power Automate was tricky when I tried it last time.