How to use ChessX to search for a given position in my database

I am confused about how to use ChessX to find games containing a given board position.

I have a database ("Lichess Elite") of games I downloaded, millions of games from Lichess.  I can see the list of games.

Now I want to specify a position and have ChessX find all the games where that position is reached.

I tried Game > New to set up the position, but it says "this database is read only".

No problem: I switch to the built-in database called "Clipboard" where I create a new game and play a few moves to reach the position I want.  I click on Find > Find Position (Ctrl+Shift+B).

But when I try to search the database for that position, ChessX only searches the "Clipboard" database (containing that one game) rather than the Lichess Elite database.  When I switch to the Lichess Elite database, the board switches to a different setup and the position of pieces is different (presumably the position of whatever game randomly happened to be the one I last looked at from Lichess Elite).

How do I specify a board position to look for in a read-only database, if it won't let me enter a new game?