The account filter on your transactions page now includes every account that has transactions, not just your connected transaction accounts.
Previously, if you had imported transactions via CSV, or had a mortgage or loan account set up manually, those accounts would not appear in the filter. You could see their transactions in the list, but you could not filter to view just that account's activity.
Now any account with at least one transaction appears in the filter. That includes connected accounts, manual accounts, CSV-imported accounts, and mortgage or loan accounts. Just open the filter, pick the account you want to focus on, and your transactions will update right away.