xhost has changed with RHEL 8 “xhost +” as “root” returns a “cannot open display” try this instead

Looks like you cannot run xhost as root

When I run it from my admin account that has sudo – it “xhost +” works

[mf@centos8-vm1 Downloads]$ xhost +
access control disabled, clients can connect from any host
[mf@centos8-vm1 Downloads]$ sudo su -
[sudo] password for mf:
[root@centos8-vm1 ~]# xhost +
xhost:  unable to open display ""

xhost +SI:localuser:oracle
# then to test
sudo su - oracle
xterm

BTW if XWindows is not loaded on your linux app for RHEL or clones you can go here, download the RPM and do a yum install like this:

https://rpmfind.net/linux/rpm2html/search.php?query=xorg-x11-apps&submit=Search+...&system=&arch=

$ yum install org-x11-apps-7.7-21.el8.x86_64.rpm
# or
yum install xorg-x11-apps