Mac mini doesn't restart successfully, but has no problem with a power-on start

This question has been asked previously but was not answered. I would like to know if there is a solution to the problem.

My Late 2012 Mac mini (Macmini6,1) does not restart successfully since replacing the HDD with a SSD. On a restart, it comes up with a grey screen with a slashed-out circle. I must power-down then do a power-on start.

The system has 16GB of RAM (I believe it's original to the unit, manufacturer code 0x0198), a 1 TB SDD that I have added (WD Blue SA510), and is running the highest OS available, macOS Catalina 10.15.7.

I initially did a clean install onto new SSD, formatted/initialized to APFS. I experienced the behavior described above. Because it would not restart successfully, I thought I would try cloning the original hard drive instead of a clean install. Maybe there were some cache or other files that it wanted to see? I don't remember what utility I used to clone it, but upon completion, I tested several scenarios and it all yielded the same result, that after a prolonged attempt to reboot, with the progress bar going just over halfway in about 1.5-2 minutes, I then see the general prohibition "circle with a slash" symbol. Shutdown and then power-on results in a quick start, around 30 seconds to the desktop, always successful.

So with both a clean install and a clone from the HDD it gives the same results. I've run the procedure outlined in another tech article using OnyX to clean files, run disk first aid to check file permissions, and reset the parameter ram. Nothing has changed the situation.

Any further thoughts or suggestions?