Lock Forums
With this feature, you can lock all (or only some) forums and prevent use of new topic or new reply forms with customized messages.
This feature supports forum override settings, and you can control locking process and lock message for each forum, and selectively lock only some forums.
Settings for Topic Form
You can enable locking, but you can also select roles that can still post in locked forums, allowing keymasters to post even if regular users can’t. And, you have a field to set the lock message to show instead of the topic form.

Settings for Reply Form
These settings are exactly the same as for the topic form.
Locking of all forums or only some forums
Two main ways to use this is to lock all forums, or lock some forums only. To handle that, you have very powerful forum override settings metabox in all forums on the admin side.
Lock all forums
If you don’t use the forums overrides, using main Lock Forums settings, and using Disable Topic Form or Disable Reply Form will disable them for every forum. And, using forum overrides, you can disable locking for some forums only.
Locking some forums
For this, we need forums overrides, and in main Lock Forums settings do not enable Disable Topic Form and Disable Reply Form options. Now, with forums override metabox, you can disable just some forums you want locked.