Hi @gregcaporaso and @lizgehret
Thank you for your help, I was too much attracted by the "To learn how to install" link on the main q2-boots library page, and did completely overlook the top right corner! 
After a clean re-install of q2-amplicon-2024.10, I was able to 'update' with q2-boots.
The reason, why I had to start over with a new amplicon installation is due to the third-party plugins gemelli and empress, where I have to use a workaround to get them installed (see: Qiime2 Library Compatibility - #8 by colinbrislawn).
After q2-amplicon and q2-boots, I was able to get q2-gemelli and q2-empress also running.
The new library website is great (including the videos!), I just have to get used to it!
Best,