My extended monitor works like only one monitor just attached to the main display after upgrading ios to Sonoma 14.4.1

As the above title explains, it does not show the dock on the extended monitor and work like only one screen just attached to the main display. There was no problem before upgrading it to 14.4.1 from 14.4.0. it showed a separate dock when I moved a cursor to the extended (external) monitor at its bottom and it also could be used as a separate full screen mode.

It recognizes the external monitor as the extended display but I don't know why it works like an extended main display instead of a separate extended display.

Is it a problem of the new update or only my issue?