where to find out when new RS guidebooks will be available

A new Portugal guidebook will be available January 2023 according to this page:
https://store.ricksteves.com/shop/p/portugal-guidebook

For all his books when you go to the book page click "Product Details" and it'll tell you when the next edition will be out.

But to add....
Even if a book is the latest-and-greatest doesn't mean all of the info in it will be current. Closings for refurbishments, changes in hours and entry fees, changes in tourist sightseeing and transport passes, hotel and restaurant closings, etc. can occur after a book has gone to print.

Especially for sightseeing plans, it's always best to reference the websites for the attractions themselves for the most current information.

A guidebook is just that, a GUIDE. It used to be the only reliable, authoritative way to get travel info. Now it should be thought of as an overall guide, a rough outline. You read it and say, I think those three things sound interesting. Then you actually research them.

If he says go to the Orsay, you read his description of the art there and his suggested itineraries and how long you should plan to be there. But then you go to the Orsay website and find out times and prices, and possible restrictions. If he recommends a pass, you research if a) that pass would still work and b) if it even exists anymore. Paper can't keep up with electrons.

Thanks for all the excellent input. As it turns out, I already had the 2017 version so I will let that guide my early planning. Thanks again.

His self guided walks stay the same (I think?), so even an older book is pretty useful for that.