I can enter the size and everything, but when I click the Create button nothing happens.
Which version of InDesign and OS?
You normally create a new document: File > New > Document, you then enter the specifications and click OK.
Yep - I've been using it for years. For some reason today I can't create a new file. I have restarted my mac and ID and it still isn't working. The only thing I can do is open an existing file and edit that and save as a new file.
OS 10.15.7, ID 16.0
It might be worth resetting your InDesign preferences.
That worked - thank you!