Rebooting via the Portal is normally a better option than rebooting from the OS. In certain circumstances a "shutdown -Fr" or "init 6" may be unable to get the cpu cycles required to actually achieve the reboot. The Portal will attempt a clean shutdown but if it doesn't complete in a timely manner (I believe this is 10 minutes) then it will force a shutdown/restart.
The reboot option is available via the three dots at the far right of the "Node" section. Be mindful of the floating "Support" button that can obscure the three dots....
Overview - Oracle Base Database - DB Systems - DB System Details - Nodes
Virtual Machine
Bare Metal
Exadata
Default is VM.Standard2.4 (21-Dec-2021)
https://docs.oracle.com/en-us/iaas/Content/Database/Concepts/overview.htm#vmShapesTotal node count
Oracle Database software edition
VCN
Client subnet
Use network security groups (NSG) ?
Hostname prefix
Private IP Address (optional)
Fault Domain
Time zone
TODO
TODO