By default, WooCommerce does not enable a fixed amount discount such as $5 off, $10 off, or $15 off, etc, from the cart's total.
How can I give such a discount when creating a new order from the admin?
I have looked at many plugins but none enable this type of discount.
NOTE: The discount should be usable without any conditions and I should be able to apply it to any order I feel like discounting.
You don't need any plugins for this as Woocommerce handles the functionality out of the box. Goto
Woocommerce > Coupons
and set the discount type to "fixed cart discount". Make sure that coupons are enabled viaWoocommerce > Settings > Checkout
(select the "enable the use of coupons" checkbox) beforehand though.