Environment

Windows 10 pro with Hyper-V
Vagrant v.2.2.6

Status

Trying to starting homestead VM with SMB shared folders via Powershell and admin user, but with no luck.

Shared 'Site' folder and created a dedicated user (usr:vagrant, pwd:vagrant) with full access to shared folder.

Really struggling on this.

Set shared folder as Sites\mysite (without complete path) since i'm sharing just this specific folder, is it right?

Error

PS C:\Users\sgrat\Desktop\Sites\Homestead> vagrant up --provision
Bringing machine 'homestead' up with 'hyperv' provider...
==> homestead: Verifying Hyper-V is enabled...
==> homestead: Verifying Hyper-V is accessible...
    homestead: Configuring the VM...
==> homestead: Starting the machine...
An error occurred while executing a PowerShell script. This error
is shown below. Please read the error message and see if this is
a configuration error with your system. If it is not, then please
report a bug.

Script: start_vm.ps1
Error:

Failed to start VM 'homestead' failed to start.

Synthetic SCSI Controller (Instance ID 480D9BCD-B214-461F-976E-2A9A546F9BB8): Failed to Power on with Error 'General access denied error'.

 Account does not have permission to open attachment 'C:\Users\sgrat\Desktop\Sites\Homestead\.vagrant\machines\homestead\hyperv\Virtual Hard Disks\ubuntu-18.04-amd64.vhdx'. Error: 'General access denied error'.

'homestead' failed to start. (Virtual machine ID 555B1C43-AC2B-4B9C-A9B2-94BF40753C40)

'homestead' Synthetic SCSI Controller (Instance ID 480D9BCD-B214-461F-976E-2A9A546F9BB8): Failed to Power on with Error 'General access denied error' (0x80070005). (Virtual machine ID 555B1C43-AC2B-4B9C-A9B2-94BF40753C40)

'homestead':  Account does not have permission to open attachment 'C:\Users\sgrat\Desktop\Sites\Homestead\.vagrant\machines\homestead\hyperv\Virtual Hard Disks\ubuntu-18.04-amd64.vhdx'. Error: 'General access denied error' (0x80070005). (Virtual machine ID 555B1C43-AC2B-4B9C-A9B2-94BF40753C40)

Homestead.yaml

ip: "192.168.10.10"
memory: 2048
cpus: 2
provider: hyperv

authorize: c:/Users/sgrat/.ssh/id_rsa.pub

keys:
    - c:/Users/sgrat/.ssh/id_rsa

folders:
    - map: Sites\mysite
      to: /home/vagrant/mysite
      php: '7.2'
      type: "smb"
      smb_host: 127.0.0.1
      smb_username: vagrant
      smb_password: vagrant

sites:
    - map: mysite.test
      to: /home/vagrant/mysite

databases:
    - mysitedb

features:
    - mariadb: true
    - ohmyzsh: false
    - webdriver: false

I cannot speak to the validity of using relative file paths, I just remember I had some issues when I did not use complete. I am using Git Bash, but other than that same setup as you: Win 10, Hyper-V, Vagrant 2.2.6.

Here is my Homestead.yaml file:

---
ip: "192.168.10.10"
memory: 2048
cpus: 2
provider: virtualbox

authorize: ~/.ssh/id_rsa.pub

keys:
    - ~/.ssh/id_rsa

folders:
    - map: C:\Users\leif.lundberg\code
      to: /home/vagrant/code
      type: "nfs"

sites:
    - map: homestead.test
      to: /home/vagrant/code/symfobase/public

databases:
    - homestead

features:
    - mariadb: false

Also, I do not know if your keys mapping is correct and may cause an issue using forwardslash "/" instead of backslash "\".