Ssh port connection error

Step 1: Check if the ports are filtered or closed using the command:
$ sudo nmap -sS -sU -PN -p 22 <instance public ip>

If there are firewalls blocking the traffic, the output will look something like this:

$ sudo nmap -sS -sU -PN -p 22 8.8.8.8
Starting Nmap 7.80 ( https://nmap.org ) at 2023-04-02 17:16 UTC
Nmap scan report for dns.google (8.8.8.8)
Host is up.

PORT   STATE         SERVICE
22/tcp filtered      ssh
22/udp open|filtered ssh

If this is the case, I believe there are OS level firewalls that are preventing the traffic on port 22. You can review the instance's Console Logs to check if there are any log entries such as:

Starting ufw..
.
.
ufw is running. 

If the ports are Open, then can you please provide more details as to how you are trying to login to the instance and what are the exact commands you are using. Also, please try logging in to the instance using terminal and command:
$ ssh -i <path_to_key_pair> ubuntu@<public_ip> -vvv

Based on the output, I will be able to make further suggestions to troubleshoot the issue.

Hope this helps.