need a powershell script to display all office 365 public groups

The type of Group is shown when you list them via the Get-UnifiedGroup cmdlet or the graph API calls, so all the information you need is readily available. Here's an example:

Get-UnifiedGroup | ? {$_.AccessType -eq "Public"}

And if you need anything more out of it, I'm sure there are multiple samples available online, so just look them up.