What does P0300 OBD trouble code mean and?

Random OR Multiple Cylinder Missfire

It means you have several cylinders not running correct.

Be carefull! you can spend huge money and not fix this!

1st, Compresion test ond fresh spark plugs, check and replace Air cleaner if needed. Be aware that things like worn out camshaft lobes can cause this so if this is easy to check, do that before moving to # 2

2nd Pay a good tech with a scan tool that can see the sensors and engine run condition in real time to diagnose it.