Having used my phone for most of the day today, randomly and immediately following a phonemail I lost all reception and my phone showed No SIM card message. Didn't drop it or get it wet or anything, I have a Galaxy S20 and its only 4 or 5 months old. I've tried everything, all the tips etc and coincidentally a software update was due - ran that by tethering to my work phone, and that didn't solve it. Tried another SIM in my phone, worked fine. Tried my SIM in another phone, failed to recognise. The phone was literally in my hand when the SIM card failed.
Unfortunately I resorted to the factory reset on my phone, lost all my apps etc, and can't access passwords either. Biggest problem is that since resetting my phone I can't get into Samsung cloud etc to restore anything as the log in process involves sending a text / code to my phone, which is useless without a working SIM.
Thanks for your post and I am sorry to hear this, it sounds like there is an issue with the SIM, I can get this ordered for you I will drop you a private message, keep an eye out for the purple envelope