Actually, as of today, that article doesn't help. I almost linked to it this past weekend, Laszlo until I saw that it only helps people who are upgrading to Sierra.
If I read between the lines, it appears that Giacomo must be able to download the complete AC 20 and AC 19 packages that have already been updated to the latest builds in order to install. Just a guess.
Giacomo, I think you should contact technical support for Graphisoft Italy with your question and possibly a link to an updated installation package... and hopefully Graphisoft HQ will update the Sierra page with more information soon.
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AC 28 USA and earlier • macOS Sonoma 14.7.1, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB