"I will untick User Session, if that's what you mean."
That's not necessary to untick. It just start VM automatic in Enhanced mode if it's working at all.
It's been 4 - 5 years since I actively use virtual machines with enhance mode so I don't remember all requirements.
One thing that can prevent enhanced mode is using Home edition as quest OS in VM.
"Enhanced session mode isn't available for generation 1 (unless Windows 10 Pro, Education, or Enterprise) virtual machines"
Turn On or Off Hyper-V Enhanced Session Mode in Windows 10 | Tutorials (tenforums.com)