Create firmware partition for macOS to be installed Here is what I did. I removed my internal SSD from my MacBook and now I am using an external SSD (a Samsung SSD T5) with macOS on it. Currently I have Mac OS X 10.9.5 installed on it.

I want to upgrade that to the current version version of macOS (Catalina). While doing so, I got the error below:

You may not install to this partition because the computer is missing a firmware partition.

How can I fix this issue so I can use my external SSD?
possible that I'm wrong, but even if it works, Apple does not provide this mode of operation and when it makes a major update.  It checks the compatibility of the material.  But in your configuration, you do not have an internal disk.  So no firmware at the place where Apple is looking for it.
Possible that if you put a disk and you do your update on the ssd, it could work. (if Catalina is supported of your mac ...)