When GIMP 2.10 came along I went with the portable version. Can this be upgraded to 2.10.6 without losing all the things I've added to my earlier version?
I have installed the full version 2.10.6 but get a succession of errors as I enter Like:
The procedure entrypoint pthread_np could not be located in the dynamic link library it then refers to a folder and file that does exist. Suggestions gratefully received.

You should be fine using a newer Gimp 2.10.6 portable version. To be on the safe side backup your user files first. I always keep a backup of the "2.10" folder with all the scripts, plugins, patterns etc....

I uninstalled 2.10.6, deleted all Gimp files remaining, reinstalled, and still get these messages....?

Which "portable" pack are you trying to install?
Installing Samj's portable 2.10.6 is quite easy.
just in case https://samjcreations.blogspot.com/2018 ... -bits.html

Confusing you with two issues:
I have Samj's portable version 2.10.2 working very well. Can I upgrade this leaving all my "additions"

The other issue issue is I tried the full 2.10.6 install again but still get all the errors on entry.

Portable packs are self-contained.
Hence you can download/unpack the new version 2.10.6.
Try it "nacked", to see it it works.
Then open side by side the Preferences folders of 2.10.2 and the one of the new 2.10.6.
Copy and paste the added resources (it's quick, I do it at each Samj's release).
On the new one re-link the plug-ins folders you certainly keep outside using the traditional:
- open gimp, Edit/Preferences/Folders/Plug-ins/add the same you added in 2.10.2
also this step is quick

About the second question, related to the std gimp official release, I have nothing to say, because since 2.10 was out I use samj's packs.
I will come back to the official (replacing my current 2.8) when the situation will be more stable and complete (for instance, with the pdb for gegl functions)

Thanks for your help