Before getting into the intricacies of the Apple/intel Thunderbolt 3 port and it's spotty compatibility with the abundance of past and present native USB1/2/3 Hard Drives, try the following settings in Energy Saver;
Uncheck putting hard drives to sleep
Check prevent Mac from sleeping when display is off
NO power nap
Instead of native USB 3.1 ports, your 2020 MBP is equipped with Thunderbolt 3 ports that share USB-C connectors with USB, supports USB 3.1 Gen 2, and may require special "active" cables for cable lengths over 0.5 meters (1.5 feet). That being said, start by using cables no longer than 0.5 meters (1.5 feet).
If you still experience problems, make sure to only connect ONE external HDD at a time to test individual drive compatibility and use an external power supply for the external HDD if that option is available for your unit(s).
Still having problems? Purchase an Externally Powered USB 3.x Hub as this has solved the problem for many users. Connect one drive at a time to test compatibility before attempting the connection of multiple drives.
In my 40 years as a MAC user (prior Apple II/III user) I have ridden the bucking bronco of USB compatibility between USB vs Thunderbolt, USB vs FireWire, and even USB vs USB on the PC side. Even carefully selecting components that are listed in the manufacturers 'Tested Devices' list does not necessarily insure compatibility! I imagine that with 26 years in the Mac camp, your external drives probably run the gamut between USB 1, 2, and 3 interfaces in which each individual drive may or may not implement the USB protocol being used correctly.
As you can see, testing a brand new interface (Thunderbolt) that claims to be backwards compatible with current/older interfaces (USB1,2,3/DisplayPort) cannot possibly be tested with the hundreds of thousands of USB external HDDs and USB external HDD enclosures that have saturated the market since the latter part of the 1990's.
Even if your particular problem(s) cannot be solved, perhaps some of what has been suggested can help alleviate the problem, and if so please come back and post your findings so others can learn from them. Good luck to you, and hope that something here helps you understand what 'compatibility' means in the wild world of computing!
