Yes, this is a big problem. Crash bugs need to be fixed. A workaround here can be closing and reopening the home city but the natural flow is to take a new card and go straight to the Deck Builder, where deselecting the new card from the broken selection state crashes the game.
I also reported the bug here: [AOE3 DE] [BUG] Campaign Reward Home City Cards Crash Game - Broken Selection State
And here’s what it looks like. If you click the “selected” card that is missing from the selection, the game crashes. This is 100% reproducible by following the steps you gave in this bug report (which are really good, although I think the button to click on is Deck Builder).
