When I need to add a series of transactions in one account, I click the dropdown arrow next to "Add to Cash" and choose the account, and the page filters to only show transactions in that account as well as inserting the "create transaction" form at the top of the transaction list ... but once I've added the transaction, to add the next one in the same account I have to click the dropdown arrow again.

The "Add to" button should default to "Cash" (or whatever is selected in settings) when no filter is active or the active filter doesn't include any "in account" criterion, but when there is a filter that limits visible transactions to just a single account, the "Add to" button should default to that account instead.

(I'm pretty sure Lunch Money used to default to either "the currently filtered account" or "the account used for the last manually-entered transaction", back when I was first getting my pre-Mint transactions into the system, but when I started using the "add transaction" feature regularly again earlier this year I was disappointed to see the button now always defaults to "Cash".)