The FileVault security system, introduced many years ago to macOS, prevents someone from starting up or restarting your computer and gaining access to its startup volume, which is encrypted. (FileVault handled the encryption in its early days, but it’s now handled in hardware and always enabled with any Intel Mac with a T2 Security Ship and with all Apple silicon M-series Macs.)
This introduces a problem if you’re using remote screen access to use your Mac. If you need to make a change that requires rebooting your Mac, it will go right back to the FileVault login screen, which cannot be accessed through remote-control software. The password has to be entered at that screen to unlock the startup drive and to boot into macOS.
Read more at Macworld.com