Good morning, ironbear119!
I haven't seen a lot of traffic on this topic after the iOS 12 update was rolled out. Have you tried following these steps yet: If you get an alert about the SIM card in your iPhone - Apple Support? Give those steps a shot and let me know if you still see the SIM error.
Happy Monday! Just checking in to see if you had a chance to try the steps I listed a few days ago. Keep me updated if that cleared the SIM alert.
I tried those steps, still didn’t work for a few days then one day it started working again, thanks for your help