A SOLUTION!
At home I can use Snip&Sketch but no Snip appears in order to annotate it. On my work PC this operates as it should do. Both PC's are up to date with Win10 and Edge browser.
I have now found a solution!
After taking the Snip hit Win-A. This will open up a bar on the right which contains your Snip. Click on it and it will open in the S&S window to be annotated!
Not only that, but this option remains usable long after taking the Snip and does not need to be done right away.
Hope that helps someone, because this was driving me crazy.