Ya know.
I have been having a little argument with one other regular contributor here, for awhile, about whether external drives being used with iPads need to be formatted with a Mac or PC and in theory, it should not make any difference, but, in practice, Apple and Microsoft maybe have slightly different drive formatting code that make using a Windows PC problematic for formatting external drives to be used with any Apple devices or computers.
I have seen in the past that formatting external drives for use with iPad does NOT work, most times, when formatting such drives, using a Windows PC.
You may need to seek out someone you know with a Mac to help you reformat that drive using a Mac
OR
You need to search online for your nearest, “local” Apple store location and call contact phone numbers and call to make an appointment to have that external drive reformatted using a Mac, instead.
The same drive formats apply.
Mac native drive formats, Fat 32 or Ex Fat, should still all apply.