I don't think this change has been highlighted on the forum yet, though I've mentioned it in a couple of posts.
In the past we recommended that visitors to Barcelona buy the T10 transit card for buses and the Metro. It was good for ten rides and could be shared by multiple travelers. The T10 is no longer being sold and can be used only until the end of this month.
The replacement is the T-Casual card. The current price is 11.35 euros for Zone 1, and it, too, is good for ten rides. However, it cannot be shared. Details are here: https://www.tmb.cat/en/barcelona-fares-metro-bus/single-and-integrated/t-casual
The zone map is here: https://www.tmb.cat/en/barcelona-fares-metro-bus/single-and-integrated/zone-map. It appears that everywhere a tourist would think of as "in Barcelona" falls within Zone 1.