Why does my Mac's menu bar turn black on startup, and how do I fix it?

Your screen shot shows "AntiVirus for Mac" in the upper left. What is that? Why would you install anti virus software on a Mac, what have you installed, and such software does not add value and has been known to create anomalies on Macs where it is installed.

Shutdown the computer

Disconnect all external devices

Restart in Safe Mode.

There are instructions for Intel Computers and Apple Silicon Computers

Yours is iMac 24″, macOS 15.3 Apple Silicon

This will perform a Disk Repair, clear cache files and only load Apple Software, extensions and fonts.

The boot up will be slow and can take some time - Normal.

Safe Mode will also eliminate Third Party Software, extensions and drivers from loading. It will only load the Minimum amount of Core Apple Processes to allow the the computer to function at a reduced Level of Performance 

Does the issue present in this mode ?

" AntiVirus for Mac " and " Bitdefender " both on the same computer at the same time ?

Once this type of software are installed and embedded into the computer 

Start Over from Scratch 

Heavy Handed - Yes ?

Effective in removing the AV Software - Yes 

Sometimes these useless applications install Kernel Extensions that get so embedded into the Operating System it is impossible you get them out

For Apple Silicon computer >> Use Disk Utility to erase a Mac with Apple silicon.

For Apple Intel computers >>   Use Disk Utility to erase an Intel-based Mac followed by How to reinstall macOS

Always make a Time Machine Backup  before  proceeding 

If going this route - I suggest Not using Startup Assist to migrate everything back.

This will probably Re-Introduce ( the useless applications ) back into the Operating System 

You can try the previous suggestion re Reduce Transparency

Report back if you would

Though I am baffled by the reference to Menu Bar

M3 MBA Sequoia 15.3.2 from OFF to On

Only One User account on the computer , Mine

The only menu bar I see, refer image below

Keyboard Language, Battery and the last icon to Shutdown, Restart etc

gaston278 wrote:

In safe mode, no problem. But when restarting the normal way, the problem persists.

Baring a Hardware issue which is possible though not likely

To avoid a session of Q&A, Q&A  and Q&A  

Download the Application Etrecheck ( External Link ) directly from the Developer.

This is a Diagnostic Tool that makes no changes to the computer.

It makes a coherent and readable inventory of both the Hardware and Software used on the computer 

The application is free or paid for added features. 

The Report will Not Reveal Any Personal Information. 

Post back the Full Report - copy and paste - >>>> using the Additional Text Icon  <<<<

If you choose to run and post the report now or laters

Someone will be willing to have a good look at the report

We may even offer some possible solutions

gaston278 wrote:

menu bar on macos turns black on start up and log in must be clicked to proceed

[Re-Titled By Moderator]

What does this mean? "log in must be clicked to proceed"?

When your mac starts, you are supposed to login. What exactly is not working as expected?

No curser in the Log In Field ?

You may Require to move the Mouse ( Curser ) into the Password Field

One (1 ) user account on this computer

If Reduce Transparency is set in Accessibility System Settings, the menu bar will be black.

The menu bar text color is dependent on the background color on your desktop.