Hello there! I am Charity, I'm an Independent Advisor and a Microsoft user like you.
I'm glad to help you today!
Since you have tried almost all troubleshooting steps, let's try disabling USB Selective Suspend Go to Control Panel > Power Options > Change plan settings > Change advanced power settings. Expand USB settings > USB selective suspend setting, and set it to Disabled.
If issues still persist, this could most likely be a hardware issue. Does the issue still persist even when on battery? or does it make any difference at all? Have you also tried cleaning all the USB ports on your Lenovo slim 7i?