System does not boot from RAID after power outage

Hello everyone, happy owner of DELL PowerEdge T140 here.

The operating system (Windows Server 2016) had been working fine for more than 5 years, but now it is not booting after a power outage (scr1). I don't see the option to boot from RAID in the Boot menu (scr2). As far as I understand, controller settings are OK (scr3), and physical drives are online (src4).

I don't remember the previous UEFI config, maybe I should change the SATA settings to RAID mode (scr5)? But after I changed the AHCI mode to RAID mode, I received a warning about potential data loss (scr6). Does it mean data loss on drives or in BIOS settings? Any advice on how I can get my OS to boot?

PS. Sorry if the question is too dumb, I haven't worked with any enterprise equipment or RAID controllers before.