Get-MsolDevice RegisteredOwners export to CSV fails - powershell

Question

I've written a simple script that is attempting to use the input from a source CSV file containing ObjectID's in a column and then exporting the following information; DisplayName, DeviceTrustType, RegisteredOwners, ApproximateLastLoginTimeStamp using the Get-MsolDevice command.
Here's the code I've got so far:
Connect-MsolService
Connect-AzureAD
Get-AzureADDevice -All $True | Select ObjectID | Export-Csv "C:\temp\Project\IntuneDevices\AllAADObjectIDs.csv" -noType
$allobjects = Import-Csv "C:\temp\Project\IntuneDevices\AllAADObjectIDs.csv"
ForEach ($line in $allobjects)
{
Get-MsolDevice -ObjectID $line.ObjectId | Select DisplayName,DeviceTrustType,RegisteredOwners,ApproximateLastLogonTimestamp| Export-Csv -Path "C:\temp\Project\IntuneDevices\Final.csv" -Append -NoTypeInformation
}
The problem is that when I open Final.csv the entry for RegisteredOwners shows up as System.Collections.Generic.List`1[System.String]
When I simply run the command from the terminal without exporting to a CSV so the oputput is displayed on the screen it looks fine, I see the RegisteredOwner listed in curly brackets like {username#domain.org}.
I've read that is because the output for RegisteredOwners is a list item and not simple text like the rest of the output, but I'm having a heck of time converting it inline.
I've tried things like inserting
Select -Property DisplayName,#{ n='RegisteredOwners'; e={ $_.RegisteredOwners -join ';' } }
But that errors during the run no matter the variations I've tried with it.
Any help with this would be greatly appreciated as I've searched and tried multiple solutions but none are working for me.
TIA

Answer 1

Thanks for pushing me in the right direction Bender, turns out I must have had some sort of syntax error I didn't understand. Here is the final code and it's working as intended.
## Script to collect all AzureAD registered devices, their trust type, and their owner.
## Connect to AzureAD and MSOL
Connect-MsolService
Connect-AzureAD
## Get all devices filtering their ObjectID
Get-AzureADDevice -All $True | Select ObjectID | Export-Csv "C:\temp\Project\IntuneDevices\AllAADObjectIDs.csv" -noType
## Create the variable from the expoted Csv
$allobjects = Import-Csv "C:\temp\Project\IntuneDevices\AllAADObjectIDs.csv"
## Create a new file using Column 1 of allobjects.csv entries to suss the information required for each device
ForEach ($line in $allobjects)
{
Get-MsolDevice -ObjectID $line.ObjectId | Select DisplayName,DeviceTrustType,#{ n='RegisteredOwners'; e={ $_.RegisteredOwners -join ';' } },ApproximateLastLogonTimestamp | Export-Csv -Path "C:\temp\Project\IntuneDevices\Final.csv" -Append -NoTypeInformation
}