Ubuntu installed, now sign things for Secure Boot

[mahesh]

I used Install Ubuntu desktop to install Ubuntu into a portable drive. When I try it I get:

Code:
error: /boot/vmlinuz-5.11.0-41-generic has invalid signature
error: you need to load the kernel first.

Many people just disable Secure Boot but that applies to all operating systems in the system so I do not want that.

I have been using Windows 10 for two decades. I am a developer. I am ready to switch to Linux. I have installed Ubuntu in a thumb drive and I have created a Puppy Linux in a thumb drive. So then I tried using the Ubuntu thumb drive to install Ubuntu in a USB portable drive, but I cannot boot that.

I found How to sign things for Secure Boot but I am not sure how much of that, if any, can be done using Windows Subsystem for Linux. I have Ubuntu on a USB thumb drive if that will work and if WSL will not. I have gotten to the Certificates in shim section; I have MOK.priv and MOK.der files in my WSL's user directory. After that the instructions include restarting the system and messing with the kernel so I suspect I cannot use WSL to do that much at least. WSL cannot access the files in the Ubuntu in the portable drive. Is there a chance that the Ubuntu on the portable drive is good and I just have to do the secure boot signing? If so then how do I proceed; what system do I need to use to proceed?

Am I correct that the Install Ubuntu desktop instructions should include something about this?

I first posted this question in Ubuntu installed, now sign things for Secure Boot and one response says I have done an incomplete install of Ubuntu but there is not much help otherwise.