How to reverse the effect of this Powershell command?
The command you've executed makes a new Firewall Rule. To delete that rule, Open Windows Defender Firewall with Advanced security (You can search for it in the search box). Now, go on Outbound Rules. Here, look for a rule named as OpenSSH Client (Outbound) and delete it.
Alternatively, you can execute Remove-NetFirewallRule -DisplayName "OpenSSH Client (Outbound)" on your powershell. Please note you will need an elevated PS to execute this command.