Hi @david-p,
Yes you can simulate an 8k virtual monitor with spacedesk.
Just enable the videowall mode, then create a video wall by assigning a client to a wall.
The default dimension of a spacedesk video wall is 4K (3840×2160) but you can modify it and set an 8K resolution.
For further assistance, please refer to the chapter Videowall Configuration in the user manual https://forum.spacedesk.netuser-manual/#item_619.