Is it ok use 18W Fast charger to iPad 7th generation?
Is it ok to use 18W USB C Lightning cable to charge iPad 7th generation?
Yes.
When used with a Lightning to USB-C cable, the Apple 18W USB-C Power Adapter is fully compatible with your iPad7.
Your iPad7 does not support USB-PD Fast Charging, but will charge at its maximum supported rate - 12W (2.4A @5V).