Looking for stuff to print, I saw this great idea by herold76:
https://www.thingiverse.com/thing:4312952

But as the speaker was not available for me, i redesigned my own version for this:
https://de.aliexpress.com/item/1005003151926071.html

I did not really manage to make the Lego fit tightly, but with a little support from below, everything holds. May depend on your printer...

Now the "Papa Kackfrosch" ("Papa shit frog") is said by the robot and only the laughter comes from the childrens room.

FreeCAD-File attached.

Update 05.11.2022:

This looks way more professional :

https://www.printables.com/model/310475-lego-boost-loudspeaker-holder/files