Why our SharePoint Online lists do not track any save conflicts when multiple users modify the same

As I know that SharePoint built-in list forms provide built-in concurrent conflict handling. So let say UserA and UserB access the same list item >> and UserA edit and submit the changes, then when UserB try to submit the form, UserB will get a save conflict error...

But inside our tenant this is not happening where UserB can save his/her changes and override UserA changes without getting any error message?? so has SharePoint Online change this behavior recently? and is there a way to reenable this inside our tenant?

Thanks