Yours is a common complaint. The Scribble feature that you are using is seemingly a CPU-intensive process - that causes the iPad to consume available battery charge and warm the iPad considerably more than some users anticipate.
You might be advised to seek assistance directly from Apple Support. You can contact the Support Team using the Support link at top-right or bottom-left of this page.
Alternatively, you can initiate and manage your support cases from Apple devices using the excellent Apple Support App. If not already installed, the App can be downloaded from the App Store:
https://apps.apple.com/app/apple-support/id1130498044
It is not unusual for an iPad to become warm when being used - more so when using some types of iPad case. High screen brightness and/or CPU intensive Apps will also create more heat.
The key point is that whilst your iPad may become very warm in normal use, the iPad should not become uncomfortably hot to handle. If your iPad is becoming too hot to hold, you should take your iPad along to the Genius Bar at your local Apple Store - where the technicians can examine and test your iPad for faults.
Genius Bar Reservation and Apple Support Options - Apple