How can I set the property HtmlPropertiesData of a web part

[AndyTuke]

I am trying to script a standard SP site look, as part of this I am populating a People Web Part called 'Meet the Team' with the M365 group members.
I can build a user list and it shows them in the People web part but the images dont show. Looking at the export xml of a working web part created manually, and a non working one created by PowerShell I can see that the web part object has a property called HtmlPropertiesData that isnt correct when built by code.

My code looks like below (not sure why this forum is saying there's a missing brace but there isnt, I think its the $_. it doesnt like)

$Site = Get-PNPSite -includes GroupId
$GroupId = $Site.GroupId
$Page = Get-PnPPage -Identity ResourceCentre.aspx
$PeopleWebPart = $Page.Controls | Where-Object {($.Title -eq "People") -and ($.HTMLPropertiesData -like "Meet The Team")}
$WebPartProperties = $PeopleWebPart.PropertiesJson | ConvertFrom-Json
$GroupMembers = Get-PnPMicrosoft365Group -Identity $GroupId | Get-PnPMicrosoft365GroupMembers

Write-Host ("Current users",$WebPartProperties.persons)
$WebPartProperties.persons = @()

foreach ($User in $GroupMembers) {
$WebPartProperties.persons += [PSCustomObject] @{
id = $User.UserPrincipalName
upn = $User.UserPrincipalName
role = $User.DisplayName
department = ''
phone = ''
sip = ''
aadObjectId = $User.Id
}
}

Set-PnPPageWebPart -Page $Page.Name -Identity $PeopleWebPart.InstanceId -PropertiesJson ($WebPartProperties | ConvertTo-Json -Compress)`

I have tried to update that HtmlPropertiesData using
`$HtmlPropertiesData = 'my updated html formating code'
$PeopleWebPart.HtmlPropertiesData = $HtmlPropertiesData

But it says the property is read only. ChatGPT gave me a load of nonsense to try, which didn't work unsurprisingly. I cannot find any way to update this so the People Web Part displays correctly when I build it via code