Open Port on Oracle Cloud Ubuntu (Linux)

First you have to open port on Oracle Cloud interface, after that you need to update iptables of your server to accept connection

sudo iptables -I INPUT 6 -m state --state NEW -p tcp --dport 80 -j ACCEPT
sudo iptables -I INPUT 6 -m state --state NEW -p tcp --dport 443 -j ACCEPT
sudo netfilter-persistent save

Create an Ingress Rule for your VCN

1. Open the navigation menu and click Networking, and then click Virtual Cloud Networks.
2. Select the VCN you created with your compute instance.
3. With your new VCN displayed, click <your-subnet-name> subnet link.The public subnet information is displayed with the Security Lists at the bottom of the page. A link to the Default Security List for your VCN is displayed.
4. Click the Default Security List link.The default Ingress Rules for your VCN are displayed.
5. Click Add Ingress Rules.An Add Ingress Rules dialog is displayed.
6. Fill in the ingress rule with the following information.Fill in the ingress rule as follows:
   • Stateless: Checked
   • Source Type: CIDR
   • Source CIDR: 0.0.0.0/0
   • IP Protocol: TCP
   • Source port range: (leave-blank)
   • Destination Port Range: 80
   • Description: Allow HTTP connections
   Click Add Ingress Rules. Now HTTP connections are allowed.
7. Click Add Ingress Rules.Now HTTP connections are allowed.

You have successfully created an ingress rule that makes your instance available from the internet.

Related stackoverflow answer
https://stackoverflow.com/a/64053781/643641