"No mention was made anywhere on the website."
I appreciate the expectation, and I'd like it to be that way as the Webmaster, but the process is that any incoming information needs to be vetted (either in person or otherwise) and then added to the copy/text of the book. Once we know it will be published in the next book or is a confirmed correction on something in a previously published book, then it is provided to the web crew for the online Guidebook Updates. I'm not sure if we (Web) are behind or if our Book Dept hasn't provided these changes you cited.
I do know that our Book Dept has been more than swamped trying to update of our guidebooks after the pandemic hiatus. It's like twice the work for the same volume of staff. Thanks for your patience as it will take a full cycle to get back to normal. And thank you, Dutch Traveler, for the updates you submitted! We do review all of them, so I'm sure it helped. With apologies, we aren't in a position to report back as to how each piece of info was used or applied or give status updates. Also, re seeing a line item that indicates that something will be open in 2020, that only means that bullet was added before that time. Other line items in the updates can be added later, and we wouldn't go back and change the previous "opening in 2020" reference.
To more directly answer the OP's question, the Guidebook Updates (find it in the footer) should help with the older book. If you decide to forgo the book, we do have 3 audio tours for free in our Rick Steves Audio Europe app. There would be more written walking tours in the guidebook, and I expect those largely haven't changed.
