Hello @Mohammad Daoud ,
Welcome to Microsoft QnA.
It depends on how much RAM would you need for flutter app development.
Here is the list of VMs and VM families available : VM sizes
For example, you can go for a Standard D2s v3 VM size with an 8 gb ram and 2 vCPUs.
There are also B series burstable VMs available that have 1gb, 2gb, 4gb ram sizes as well and you can give a look at it.
There are plenty of options available, depends on your requirement, choice and cost.
Hope that helps. Do let me know if you have any specific feature requirements in the VM so that I can help you further. Thank you.