Low fps, dark interiors with large migrated project

Migrated a large 30Gb project from 4.26 to Ue5. It is primarily artwork.
fps in 4.26 was 35 ish. In ue5 it is 10 fps or less. This is even before enabling lumen.
With lumen enabled the fps is just as bad and the interior of buildings has gone very very dark like no light is coming through the windows.
Get 30 fps in the editor with lumen off.
But turning lumen back off has left the interiors permanently dark. They have not resumed their previous fresh state.
When lumen was enabled it spent time creating ‘cards’. What does this mean and imply?

I also usually have very dark interiors with imported projects, ihave to set Directional light “indirect light intesity” to 50. Someone knows why and maybe the solution?

Having a similar problem with the lighting in my scene, I am going to look at some of the videos people have been dropping lately to see if they have any information on how to fix this.