https://learn.microsoft.com/en-us/powershell/module/microsoft.online.sharepoint.powershell/get-spotheme?view=sharepoint-ps
Get-SPOTheme (Microsoft.Online.SharePoint.PowerShell) | Microsoft Learn
This cmdlet returns the settings for a named existing theme, or for all uploaded themes if no name is provided. Note To support consistent branding and...
microsoft onlinegetsharepointpowershelllearn