Elevenclock

In settings there is no option to show the clock on the primary screen (only).

You are correct. You win a new Toyota Prius.

You could use something like Display Fusion which can accomodate only showing the clock on the main screen, amongst other things. But it isn’t free.
Perhaps there is a 3rd party monitor tool that is free and can do what you want.

You could suggest the feature is added at Github? As it isn’t Microsoft official, nor is it affiliated with ElevenForum.

Are you sure there is no option to do it for free in Winaero Tweaker?

When I still used Elevenclock, the last note I got from the developer (Marti Clement) was about Sept. 2024 that he was postponing all developements on that app. Why that was I don't know, but if that's still so, your 'complaint' will certainly not be honoured by a patch.

So you will have to find another way to display the clock where and how you want it.

My solution for that lays in Windhawk, where you can customize the systemtray clock as you wish. But Windhawk is a complete (freeware) package, that takes about 750 MByte space on your system drive and that is mainly used for tweaking the Windows taskbar (but has other tweaks as well).

Before I switched to Windhawk, I used StartAllBack / Start11 for tweaking the taskbar. StartAllBack has some possibility to tweak system tray clock as well, Start11 does not.

BTW. I am not sure if in Windhawk there is a possibility to program it as such, that the system tray clock only is visible on the primary screen. But it is very much programmable, so I could hardly imagine that it can't be done.