Forum Discussion
Unable to upgrade to A7 and A8 using Azure PowerShell Cmdlet -
No, there's nothing you can do about this.
I've also taken a look at the replacement command, Update-AzPowerBIEmbeddedCapacity, from the module (Az.PowerBIEmbedded) replacing AzureRM.PowerBIEmbedded and the accepted values only go as far as A6 there, too.
Given there are regional restrictions around the A7 and A8 SKUs (as noted here), my guess is that both modules only cater to the SKUs currently available in all regions, which end at A6.
If you were so inclined, you could try and work with the Power BI Embedded APIs directly using Invoke-RestMethod but that's beyond the scope of what can easily be discussed here. And if the modules are in alignment with the APIs then it probably won't make a difference anyway.
Capacities - Update - REST API (Azure Power BI Embedded) | Microsoft Docs
Cheers,
Lain