Sharepoint Properties edit form automatically switches to modern side pane to classic page form

Hi Dinesh8608422​ 

do you using classic features?

In this article in the bottom you can see "Features that automatically switch to the classic experience":

https://support.microsoft.com/en-us/office/differences-between-modern-and-classic-experiences-for-lists-and-libraries-30e1aab0-a5cc-4363-b7f2-09e2ae07d4dc?WT.mc_id=DX-MVP-5004845 

Best, Dave

Disable the modern sidebar, or switch back to classic editing mode.