No HDMI monitor display while booting up MBP?

After turning on/booting it up, I noticed the external HDMI monitor is blank black (still has a video signal) until after I log in and right before I see the desktop screen. Shouldn’t I get the display right after booting up/powering on MBP?

Detailed setup: 13(.3)" 2020; A2251 model; MWP62LL/A; Intel Core i7 MacBook Pro (2.3 GHz; quad-core 10th gen. i7 CPU; 8 MB; L3 cache (Turbo Boost up to 4.1 GHz)), 32 GB of 3733MHz LPDDR4X RAM, 2 TB PCIe-based SSD, Intel Iris Plus graphic, macOS Ventura v13.6.4, etc. from 12/29/2020. Using Apple’s USB-C Digital AV Multiport Adapter with ASUS VA27DQSB 27" 1080P monitor(HDMI) & an old USB-A (with Apple’s USB-C to USB Adapter) mouse.

Thank you for reading and hopefully answering soon. :)

I think your external display is set to be an “extended display” instead of the “main display”.

On macOS Sonoma 14.2, my external display is set as the “Main Display” in System Preferences >> Displays, and it shows the login window about 15 seconds after powering up my MacBook Pro (18,4). The MBP’s built-in display remains dark until I log in. If I switch the external display to be an “extended display”, the login screen/window appears on the built-in display and the external display is dark (which is what you describe).

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Only one standard account uses extended display (top and bottom). My admin account uses mirror. It didn’t matter which account too when I shut down/reboot to boot up to its log in screen to unlock SSD’s encrypted FileVault and log in. Is there no way to have the prelogin and boot up to show on both screens?

I have a possibly-false memory of that in earlier versions of macOS, but recently it displays the login window on one screen.

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