Dell Precision M3800 (XPS rebadged), 500gb primary SSD, 256 SSD secondary drive. Originally sold 2016. 4th generation i7 and related chips.
I used Dban (Darik' s Boot and Nuke)
https://dban.org/ to wipe the secondary drive using write all 0's single pass.
Activated the drive with windows 10 drive manager then partitioned it with drive manager.
Installed Win 7 Pro from file explorer in Win 10 until 1st reboot. Bitlocker must be turned off to continue.
A vintage Dell driver package picked up my LAN adapter allowing me to get on line.
Activation failed. I tried the automated phone option but had to call the number listed and talk to a person to get it activated.
Update and activation servers have been disabled. The rep said it is an Obsolete OS.
I downloaded and installed Drive Booster free version from Iobit.com
Running drive booster updated all drivers.
I next downloaded and installed Advanced System Care free from Iobit.com
ASC found and installed a system update.
All seemed well and I installed some scanner software.
Next I downloaded EaseUs Todo backup free, installed and preformed a backup on the drive.
Now on reboot I get Win 7 boot loader which has micro printing on this 3840 x 2160 on this screen.
Now I booted into Win 10 Pro on the primary drive and do the inplace reinstall keeping personal files and apps to get the Win 10 boot loader which scales to the resolution.
Now USB storage drive that was recognized before the Win 10 reinstall on Win 7 is no longer recognized on Win 7.
I have not tested other USB devices as the WiFi driver took over.
Conclusion: a major waste of time.
If you have a older computer that shipped with Win 7 or upgraded to Win 7 you may not experience these problems except for activation or updates.