Don't worry my guy, that's normal. If your phone heats up like 37°C to 40°C and you use your S-Pen, it will give off a burnt-ish rubber smell. If you ask me it's kinda addicting
Observe closely your phone's battery. It's abnormally giving up higher heat, and your S-Pen plastic casing is absorbing the heat. Does your S-Pen (made of plastic and parks besides the batt) look crooked? Likely, the upper portion, its plastic melting is exposed to high heat, perhaps melting.
What's you device model? I believe it's not S23U, coz it's corrected designed with special Snapdragon chipset. Cool.
KyleKyle and yours truly, are S23U users too. Mine doesn't give out any smell at all. Kyle may have the smell, but he loves it, like pork BBQ, perhaps 😜. Check any plastic (black) color deterioration. If there's none, then it's ok, but just be alerted.
Somebody here had this issue weeks ago, posted melted S-Pen photo. I will try to post the link here.
Thanks for reaching out to us in order to find out about other member's having similar experience in S Pen that has burnt rubber smell. I feel and understand what's your situation, taking care of my device too much, if I encountered the same, I will get worried too.
With limited view of what's really going on your device, I highly recommend bringing it to the nearest Samsung Service Center in your location. Rest assured that your device will undergo an assessment to pinpoint the root cause of the issue. They may guide you and offer solutions to restore it.
