I noticed that two versions of the mod package are offered on the soamigos site, normal and DLC style / new engine (Delphi11).
What's the difference, and which version should I download for GOG SoA + Patch 1.06?
(if this question has been answered already on the SoA forum, in German or English, just post a link - I haven't managed to find one).

It doesn't matter at all which version you take. The difference is that the "newer engine" is based on the new Source Code from the rerelease compiled with Delphi 10 whereas the other version is based on the old Source Code from ~2001 compiled with Delphi 4. The only difference you will recognize is that the main menu isn't centered in the old code Version.
Info:
https://soamigos.de/wbb5/forum/index.php?thread/4581-steam-gog-siege-of-avalon-modpaket-in-neuer-engine-delphi-10-4/

Thanks! I had searched your forum for "new engine", "delphi 11", "neue engine" and a few more, but apparently not for "engine" alone :-(.,

Yeah the search function sometimes isn't that effective...

Well - I'm afraid it's rather the other way around: I myself am not that effective ... :-)

But more importantly: Thanks for what you do to keep this game alive, improve it, and help players!