Greetings @davey4553 !
We see that this is your first time posting! 
Welcome to the Unreal Engine community! I’m sorry that you are having issues with Lumen in UE5. Until one of the Rock Stars of the community provide you with some great suggestions and possible solutions, please consider looking at the threads here and here. Also, what are the specs for your GPU?
Thank you for being an important part of our growing community, and I wish you the best of luck in discovering solutions for the problem you are having with Lumen! 