Installation onto external hard drive

I have installed budgie onto an external hard drive. I was looking to be able to use the os from the hard drive on different Pc’s but notice that i can only boot the os onto the PC used to install the os onto the external hard drive. When i go to other machines and try the boot menu os on the external hard drive is not available and pc just goes onto boot windows.

How do i enable being able to boot the external hard drive onto other pc rather than being tied to the one used to install the os???

I think the following links can help you make a portable installed system,

If you don’t want to re-install, I think it is possible to put the necessary boot structure onto the external drive, but it can be a bit tricky. If you ask in the Ubuntu Forums I think you will get detailed help from @oldfred and/or other people with long experience.