I am also having a similar issue with my S21 Ultra.
They are not going to refund or exchange the device.
Kindly check my tweet and also retweet the same.
Dear Samsung Member,
Greetings from Samsung Customer Support!
Please visit this mentioned link to resolve your device heating issue: https://www.samsung.com/in/support/mobile-devices/why-the-device-heats-up-during-use/
For further assistance, register your concern in Samsung Members Application (Open Samsung Members Application > Get help > Send Feedback > Error report/Ask questions).
Thank you for writing to Samsung.
Samsung Customer Support