I have been using the Arduino IDE ver 1.8.13 on a pretty beefed up PC running the latest release of Windows and an Arduino Mega 2560 board.
Using Serial.begin(115200); found in most examples seems to be keeping the processor VERY busy such that uploading or opening the serial monitor results in some sort of com port error or another. Taking 10-20 tries to establish communications. Cutting that speed in half helps quite a bit and at 57600…you won’t miss anything.
I am not sure that we are one the same line. But if you mean that after some time the serial gets really laggy and eventuelly crash: Then I am experiencing the same issues! My solution was to use an other program that can read serial such as Putty. That remains fast and stable on my pc even after some time!