If you below error message in your oracle VM then in both cases your mouse , xming session or many other funtionalities don’t work in oracle virtual box. Make sure you check the permission of the file and folder containing the file.

could not update ICEauthority file /var/lib/gdm/.ICEauthority

or

could not update ICEauthority file /home/oracle/.ICEauthority

This one should be owned by gdm:gdm

[root@ol6-18-rac2 ~]# ls -ltr  /var/lib/gdm/.ICEauthority
-rw-------. 1 gdm gdm 24820 Oct  6 12:22 /var/lib/gdm/.ICEauthority
[root@ol6-18-rac2 ~]#  ls -ltr  /var/lib/
drwxrwx--T. 8 gdm     gdm     4096 Oct  6 12:22 gdm

and below one should be by oracle:oinstall or oracle:dba. In my case below file was owned by oracle:oinstall but oracle folder was owned by root:oinstall somehow. So I changed folder permissions to oracle:oinstall

[root@ol6-18-rac2 ~]# ls -ltr /home/oracle/.ICEauthority
-rw-------. 1 oracle oinstall 3736 Oct  6 12:22 /home/oracle/.ICEauthority

[root@ol6-18-rac2 ~]# ls -ltr /home/
total 24
drwx------.  2 root    root     16384 May  4  2020 lost+found
drwx------. 23 shalabh shalabh   4096 May  4  2020 shalabh
drwxr-xr-x. 33 root    oinstall  4096 Oct  6 12:31 oracle


[root@ol6-18-rac2 ~]# chown -R oracle:oinstall /home/oracle


[root@ol6-18-rac2 ~]# ls -ltr /home/
total 24
drwx------.  2 root    root     16384 May  4  2020 lost+found
drwx------. 23 shalabh shalabh   4096 May  4  2020 shalabh
drwxr-xr-x. 33 oracle  oinstall  4096 Oct  6 12:31 oracle