I’ve just updated SUp to 2022 and thought it would be a simple update but alas, it appears that I have to reload in the original template file I’d created way back when and all the plugins need to be added back on which is a real pain.
Is this standard with an update like this or should I have chosen an update download?
Yes it is a standard. The main versions installs separately, and you need to set it up and install your desired Extension. While you are doing that you still can use the old version as before (unless you uninstalled it.)
There are plenty of topic about how to “migrate”.