I'm not sure what could be causing the flickering in San Sequoia, so I can't help with that, but EP13 doesn't have a folder within the Delta folder yet. You shouldn't try adding one there yourself since you'll be missing build package files that the game would expect to be there, not just world files. To install a lighting mod for EP13 you just need to place it in the "The Sims 4/EP13" folder (NOT Delta, since there's no Delta/EP13 yet). Hopefully that resolves your issue!
Viewing post in Lighting Mods: Installation Tutorial and FAQ comments
Oh my gosh - thank you so much! This is actually IMMENSELY helpful. I'm so sorry if I missed this in the instructions, I try to be thorough but sometimes my mind skims important things subconsciously. This entire time I thought I'd destroyed my game and it was forever missing the EP13 Delta file (I feel so silly). Then it must be some other mod/cc causing the flickering... thank you. I'll be re-installing your mod properly this time and then I'll sort out what else is causing the weird shadows.
I appreciate you so much!! Have a lovely rest of your day and TY AGAIN!