User Group Assignment not Working

[Bigyan_Mainali]

Active users allows to select multiple users where we are able to click option for manage groups by click three dots.

Manage group feature used to allow users to be assigned to group(s) by searching the group which is no longer working.

Is there way to assign selected multiple users to certain groups?

[#2]

Seems to work fine here, but I've noticed you seem to be getting the old UI in the screenshot. Which O365 instance is that, and have you enabled first-release at least for the admin accounts?

You can always use PowerShell for bulk operations btw, and some of them can also be performed from the Azure AD blade if you want to use an UI-based approach.