Greetings MikeR57,
For help using that accessory with your iPhone, begin by reviewing the guidance found here:
Using USB accessories with iOS and iPadOS
Starting with iOS and iPadOS, if you use USB accessories with your iPhone, iPad, or iPod touch, or if you connect your device to a Mac or PC, you might need to unlock your device for it to recognize and use the accessory. Your accessory then remains connected, even if your device is subsequently locked.
If you don’t first unlock your password-protected iOS or iPadOS device—or you haven’t unlocked and connected it to a USB accessory within the past hour—your iOS or iPadOS device won’t communicate with the accessory or computer, and in some cases, it might not charge. You might also see an alert asking you to unlock your device to use accessories.
If the USB accessory is still not recognized after you unlock your device, disconnect your device from the accessory, unlock your device, and then reconnect the accessory.
If you haven't done so already, restart your iPhone. Sometimes a restart can help resolve issues. Also, the article mentions "Administrators can control the USB Accessories setting on supervised iOS or iPadOS devices using Apple Configurator or mobile device management." To check, go to Settings > General > Profiles & Device Management. To be clear, this setting won't appear if you don't have a profile.
To confirm, are going here in the Files app to view the drive? Connect external storage devices to iPhone - Apple Support
View the contents of the drive or memory card: In a supported app (for example, Files), tap Browse at the bottom of the screen, then tap the name of the device below Locations. If you don’t see Locations, tap Browse again at the bottom of the screen.
Do you have any other issues with using accessories via Lightning cable with the iPhone?
Take care.