Given that your iPad mini6 has a USB-C port, perhaps the most straightforward solution is to use one of the many good quality USB-C hubs that incorporate both USB ports and a SD/microSD card reader. Good hubs are designed to allow simultaneous connection of a Power Adapter or PowerBank battery - this being essential for some power-hungry external drives.
Perhaps consider Kingston, Anker, Hyperdrive and Satechi - although there are many others from which to choose. A Google Search for USB-C Hubs compatible with iPad will find a number of articles and recommendations. Speaking of personal experience, the Kingston Nucleum has proven itself to be particularly flexible for the purpose that you describe - featuring twin USB3.0 Type-A, downstream USB-C and SD/microSD card slots, HDMI, plus a power pass-through USB-C port that can accept +45W from a suitable USB power source.
Be aware that external HDD are notoriously power hungry. A better solution for bulk external storage is solid-state USB and SSD. Either must be both partitioned and pre-formatted appropriately (i.e., a single partition - formatted as FAT32, exFAT, APFS or HFS+) - otherwise it cannot be accessed by iPad.
Apple do have a good USB-C to SD Card Reader, but this will not be needed if you are using a good third-party USB-C hub:
https://store.apple.com/uk/xc/product/MUFG2ZM/A