I managed to set my 2nd mail account as my new default mail account. So in Thunderbird, the previously 2nd account folder shows up on top now.
But when sending an email, the default "From" address is still picked from the previous default mail account (default identity from account), and not from the new default mail account.
I restarted Thunderbird, but the issue remains.
Do I need to change the default account for the "From" as well? If so, how can I do that? Or is it a bug?