PokerTracker

Hi devs,
When going in "Hud -> Edit HUD Options -> Advanced -> Read from Databases", I would like to pick a specific db, and unselect the current one. However I get the error "The active database must be selected."
How can I get around this ?

You will need to make the database you want to use for the HUD the active database in PokerTracker 4 via the 'Database Management' window:

Guide: Database Management (Setting the Active Database)

The active database will also be the database that hands get imported into while playing.

No, I want to review hands stored in database B, using the player data from database A (and only A to avoid duplicates in stats)
I remember it could be done in an older version of PT4 from early 2023, but now the choice of dbs to read from is restricted to necessarily include the active db, which I do not want.

Unfortunately that cannot be done since the active database must be selected. I don't see any reference to any specific change to this functionality and I've also installed some older versions and in all those I've checked the active database still needs to be selected.