iPadOS provides limited support for external Hard Disk storage.
An external HDD can be connected to your iPad with the Apple adapter appropriate for your model of iPad - if the HDD is both partitioned and formatted appropriately (i.e., a single partition - formatted as FAT32, exFAT, APFS or HFS+).
As you have already noted, for iPadOS there is no safe-eject of USB storage devices - and this becomes a potential issue where pending “writes” are cached by the drive prior to writing to the non-volatile HDD platter or SSD storage. If the drive is disconnected, or power removed, corruption can occur. This is true of all disk/device formats. For iPadOS, the safest method of dismounting the drive is to wait for all disk activity to cease - and then properly shut-down the iPad.
You should also note that the iPad is not capable of providing sufficient power to run an HDD. If the HDD does not have its own source of power - then external power must be supplied to the HDD using a connecting adapter (e.g., an Apple Lightning to USB3 Camera Adapter and Apple Charger of at least 12W) - or by connecting both the iPad and HDD to a powered USB hub capable of sourcing sufficient power for the connected storage device.
