Those temperatures are perfectly normal. These newer Intel Macs run much hotter than older models. Sometimes just moving the pointer or opening a file may cause the CPU temp to spike to 80C for a moment as the CPU core is used.
I have performed tests with our organization's Apple laptops in order to understand what temperatures are expected so I can better troubleshoot system issues. I'm not aware of any documentation detailing this behavior.
If you feel the system is running too hot, then it is likely due to some third party app which has been installed. Typical culprits are anti-virus apps, cleaning/optimizer aps, third party security software, and bittorrent/file sharing apps (first three types are not needed on a Mac). Sometimes a file system issue or an externally connected device could be causing a problem. Booting into Safe Mode should prevent third party software from automatically launching during boot & login so you should see a bit lower temperatures while "idle", but when using apps the temps will easily go up to those you have already mentioned.
You can run the Apple Diagnostics to see if any hardware issues are detected. The diagnostics are usually pretty good about alerting to any issues with the cooling system. If the diagnostics do not report an issue with the cooling system, then most likely everything is normal except for the possibilities I have already outlined.
