Do I have to format a new external hard drive for high sierra?

I agree with macjack, always reformat a new drive before using,

regardless of its original format. BTW, at this point in time with

High Sierra, make sure you format it macOS extended journaled

if it is a standard hard disk drive and if it is to be used on any

system other than High Sierra even if it is an SSD as APFS can

only be read by macOS High Sierra and APFS is not recommended

for HDD (though it will work).

Always format a new drive, whether it comes formatted for Mac or not. Drive manufacturers include utilities and drivers which are unnecessary for Mac OS and can interfere with smooth operation.