Hello ren_hom,
We have a great support article that might help with this. Please take a look at it here: Change Control Center settings on Mac - Apple Support. Follow this guidance to adjust the date & time settings on your Mac menu bar:
"The clock is always shown in the menu bar.
Click Clock Options, then choose how you want the date and time displayed.
Below Date, click the “Show date” pop-up menu, then choose either Always, When Space Allows, or Never. You can also choose whether to have the day of the week shown in the menu bar.
Below Time, choose a clock style, whether to use a 24-hour clock, and whether to display the time with seconds. You can also choose to have the time announced periodically with a voice of your choice."
If it is still not visible after checking those settings, we advise that you restart your Mac (Shut down or restart your Mac) and make sure it's fully updated (Update macOS on Mac). Once those are done, please test this issue.
If the issue persists, continue by testing to see when this behavior occurs. First, put your Mac into safe mode and test. Booting into safe mode will disable any startup and login items from automatically opening, which can help us to isolate the source of the issue further. When you do this, you’ll see some unusual behavior from the display; this is to be expected. Please follow the steps in this article: How to use safe mode on your Mac.
Next, let's see if this behavior persists in a new user account on your Mac. Testing in a new user will determine if you have a system-wide issue or if it's user-specific. Please follow these steps to make a test account that can be deleted later: Change Users & Groups settings on Mac. Once the new user account has been set up, log out of your own account then into the new one to test the issue.
Let us know how this goes, please. Thanks and take care.