Considering your 7800X3d Maximum Operating Temperature is 89c and it reached 115c, in my opinion, you PC was either almost to point of shutting down to prevent CPU and Motherboard damage or the temperature was misread by the monitoring software.
Download and install Ryzen Master and see if you get the same temperatures while playing Starfield. If you do that would indicate a CPU Cooler issue.
The Peerless Assassin CPU Cooler should be powerful enough to prevent your APU Process with a TDP Rating of 120 Watts from overheating since your Peerless is rated at 265 Watt TDP.
So either the Peerless is not installed correctly or you have poor Air circulation inside your PC.
To check for poor air circulation, remove the PC case side panel and see if the average APU processor temperature is slightly lower. If it is that would indicate poor air circulation inside your PC.
Make sure the Peerless is on tightly and secured to the surface of the APU. That you correctly applied the Thermal Paste to the surface of the APU before installing the CPU Cooler. That the fans are working correctly and at full speed when overheating. No obstructions to the CPU Cooler's fan air flow. etc.
In Radeon Settings under Performance try to create a more aggressive Fan Control profile that the fans would go full speed at a lower temperature and see if that prevents the Processor from reach 80c while playing Starfield or under any heavy loads.
EDIT: Found this article that mentions that some 7000 series processors and the 78003D Processors have a overheating issue that was supposed to have been fixed by both AMD and the Motherboard manufacturers: https://www.custompc.com/amd-ryzen-7000x3d-7800x3d-overheating-bulging-voltage-controller
So, I would follow @BillyFeltrop advise about undervolting your APU processor after reading the above article.
A statement from AMD reads:
We have root caused the issue and have already distributed a new AGESA that puts measures in place on certain power rails on AM5 motherboards to prevent the CPU from operating beyond its specification limits, including a cap on SOC voltage at 1.3V. None of these changes affect the ability of our Ryzen 7000 Series processors to overclock memory using EXPO or XMP kits or boost performance using PBO technology.
We expect all of our ODM partners to release new BIOS for their AM5 boards over the next few days. We recommend all users to check their motherboard manufacturers website and update their BIOS to ensure their system has the most up to date software for their processor.
Anyone whose CPU may have been impacted by this issue should contact AMD customer support. Our customer service team is aware of the situation and prioritizing these cases.
— AMD
