After some consultation on #debian-next IRC channel, tried to see why SecBoot CPU1 Status: 0x3040001, CPU2 Status: 0x0 message appears.
Powered off the laptop (again), this time entered BIOS, checked secure boot settings. It was disabled as suspected. Didn't change anything in BIOS, but after reboot firmware loaded and wifi works.
Not sure what happened here - made several reboots before sending this report.