We just encountered this problem (Minecraft Java Edition 1.15.2, Windows 10, NVIDEA GTX 1650). It turned out not to be a Minecraft bug, but a simple keyboard configuration accident. Were were using a gaming keyboard (Ducky Shine 3) where you can set the delay and repeat rate of letter keys using the Fn and F1-F8 function keys, and the repeat rate was set unusually high. Minecraft exhibits exactly the symptoms described in this issue if the keyboard used has an unusually high keypress repeat rate set. Use a normal text editor and hold a letter key and judge if the key's delay and repeat rate are normal. If not, make sure they are normal before using the keyboard with Minecraft. You may have to consult the keyboard's manual or check your operating system's keyboard configuration settings.
Markus Kuhn
We just encountered this problem (Minecraft Java Edition 1.15.2, Windows 10, NVIDEA GTX 1650). It turned out not to be a Minecraft bug, but a simple keyboard configuration accident. Were were using a gaming keyboard (Ducky Shine 3) where you can set the delay and repeat rate of letter keys using the Fn and F1-F8 function keys, and the repeat rate was set unusually high. Minecraft exhibits exactly the symptoms described in this issue if the keyboard used has an unusually high keypress repeat rate set. Use a normal text editor and hold a letter key and judge if the key's delay and repeat rate are normal. If not, make sure they are normal before using the keyboard with Minecraft. You may have to consult the keyboard's manual or check your operating system's keyboard configuration settings.