Hi @Sabrina
Thank you for reaching out to Microsoft Q & A Platform
The number of VM's per resource group parameter is fixed and cant be changed :
https://learn.microsoft.com/en-us/azure/azure-resource-manager/management/azure-subscription-service-limits#virtual-machines-limits---azure-resource-manager
You can try out creating Azure policy for the second use case of only creating certain types of VM's in a resource group .
Ref: https://learn.microsoft.com/en-us/azure/governance/policy/tutorials/create-and-manage
Request you to please accept the answer if this was helpful in implementing your use case .
Thanks & Regards,
Pradeep