Umm... "?action=protect at the end of the page name" is just the first step... you do need to actually to setup the protection and save it.
Don't confuse a warning with a block.
Delete the page and before delete protect.
I'm not sure if they fixed that by now, but it used to be the case if you protected it before deleting, it only blocked edits to it, it didn't block creation. There's a difference; Special:ProtectedPages and Special:ProtectedTitles are separate concepts.
Just to make it clear, there is also no particular reason to protect it before deleting. You can protect it after deletion and that is the logical order.
Yeah, I was elaborating on Aquatic Henk's misinfo.
O than idk
@Sophiedp I put that in my MediaWiki:ImportJS file, does it execute when I delete a page normally or is there a special button or page?
You should see a PowerDelete option on the edit dropdown.
All of these answers should solve this desire now.
What do you think?