No, it not what I mean. I got this problem when I changed my SIM because I changed of service provider. You could try to make a factory reset. But first, make a backup of everything that is on your phone because it will be wiped out.
I'm not sure why changing Carriers / SIM would have any effect on the way a device is running, with the only explanation I can think of, is if you're using Cellular Data, but the signal is very weak.. That MIGHT cause the device to run a BIT warmer.. but not much.
If you're talking about the Samsung Galaxy S9 (SM-G960W), it was released in 2018. It is 6 years old, and if it's still got the original battery, then I would expect it to behave like that.
Replace the battery, or replace the device with a new one.
I have the EXACT same issue with battery drain that started the day you posted this. My Samsung Galaxy S9 won't stay running for more than 2 hours. Apps vary causing drain but it is usually One UI Home and Google Play Services but it does vary. May carrier is Verizon and my other cell I use is a Pixel and also on Verizon with no issues.
Pretty sure it isn't the battery as all diagnostics pass. I believe it is an app issue but can't track it down. Find it VERY interesting the OP had the same problem starting the same day I did.
