Found out Bus powered 2.5inch HDD can't handle USB-A port
Mac mini 2018 USB-A port can't drive 2.5inch 5V, 0.75A external HDD, though it is able to handle 1TB SSD external drive.
What other devices are plugged into those two USB-A ports?
I would try the external HDD on a USB-C to USB-A adapter.
https://www.amazon.com/dp/B08Z768LCW/ref=sspa_dk_detail_1?
https://www.target.com/p/philips-usb-c-to-3-0-usb-a-female-adapter/-/A-79804275 Personally I have 4 of those Philips adapters that I use with our 2018 and Silicone Mac mini's.
I also have an old self-powered Belkin 7 port hub connected to our 2018 Mac mini for USB 2.0 devices.
That old Belkin hub has no problem powering my Logitech keyboard and mouse, an LG CD/DVD drive, a couple of Flash Drives, my iPhone for syncing and slow charging, plus an occasional bus powered external HDD if there is no available USB-C to USB-A adapter.
