Try an SMC Reset. You can try a PRAM Reset as well, but that is unlikely to have any effect for this issue.
Disconnect all external devices from the laptop in case one of them is causing a problem.
It is normal for the CPU temps to be in the 90C range when using the laptop for many workloads. The cooling system generally keeps the CPU temps somewhere in that range on anything but very light tasks where the temps may be in the 65-80C range. Even web browsing is not necessarily a "light" task since some pages cause a computer to work very hard. The only time the CPU should be throttled due to heat is when the fans are at maximum and the CPU temps exceed 100C (maybe a few degrees above on some models). You will definitely know the CPU is being throttled because the CPU speed will be at idle speeds of 800Mhz where they only produce enough heat to make the heatsink feel barely warm (if the CPU has been running at idle since being powered on).
The CPU can be throttled when there is some sort of power related issue with the system.
Have you tried booting into Safe Mode to see how it performs? If Safe Mode works fine then it most likely indicates you have an issue with some third party software that is installed which is interfering with the normal operation of macOS. Typical culprits are anti-virus apps, cleaning/optimizer apps, and third party security software. You can also run EtreCheck and post the report here so we can examine it for clues....best to run it after you have been using the laptop for a while so the report includes more information for the performance metrics section of the report.
Try running the Apple Diagnostics to see if any hardware issues are detected. The diagnostics are usually pretty good at detecting cooling system issues. Unfortunately the diagnostics don't detect most other issues.
Most times when computers run hotter than normal it is due to some third party software causing problems, or due to a hardware failure.
FYI, I have found some of our organization's Macs perform extremely slowly without any high temps, yet still has the CPU running at 2Ghz+....in those cases there is some sort of hardware issue which is not easily identified. Sometimes I may find signs of liquid damage, but other times I find no signs of liquid damage so it must be do to some component failure on the Logic Board. The Apple Diagnostics rarely have identified a problem, but having the Logic Board replaced has usually resolved the problem. You can check to see what speed the CPU is running by using the following command in the Terminal app:
sudo powermetrics | grep -i 'system average'
If this is showing the CPU speed over 800Mhz, then the CPU is not being throttled. If the problem is not due to some third party software, custom configuration setting, or external device, then it likely indicates a hardware issue with the laptop itself. Like I said, I have seen the CPU speed of 2Ghz with the system running extremely slow which ended up being a hardware issue with the laptop (temps were normal).
With a 2018+ Mac, you have an option to perform a firmware "Restore" which resets the T2 security chip & firmware. This results with the data on the internal SSD being destroyed so you will need to use Internet Recovery Mode (Command + Option + R) to reinstall macOS. Test the laptop thoroughly before installing any third party apps and before restoring from a backup. If the issue occurs with a clean install under these conditions, then it means you have some sort of hardware issue. If a clean install has no problems, then try restoring only your macOS user account(s) and test some more. You can then try restoring the apps as well from the backup, but it may be more informative to manually reinstall third party apps one at a time to see how the system responds, or you may be performing another clean install where you will manually reinstall apps.
