Powershell: extracting a comma-separated list of IPs?

I'm dealing with a .csv export from Nessus, where essentially I have a column of Host IPs and a column with Plugin IDs

My customer wants an output where, for example, Plugin X would be in a column, and then next to it would be a comma separated list of affected Host IPs, and then next to THAT would be a count of the affected Host IPs.

Pic of what I'm looking for

After importing the Nessus CSV with Powershell, I was able to start to get what I needed with this:

$allfiltered | select-object 'Host IP','Plugin ID' | Where-Object 'Plugin ID' -like "57041" | Format-Table -Property  'Plugin ID','Host IP'

This gives me an output like this:

57041     10.1.1.1
57041     10.1.1.2
57041     10.1.1.3
57041     10.1.1.4
57041     10.1.1.5
57041     10.1.1.6
57041     10.1.1.7

But as you can see, I have a long way to go to pull this into the output I need (see pic above).

I think I'm eventually going to need a for loop to get all the plugin values assessed, but I need to figure out how to essentially query for "Take all IPs that match plugin X and place them into a comma separated list" and go from there.

Can you help steer me in the right direction?

-B