Marlin 1.8.13 Compliling errors

I am wanting to upgrade an Ender 3 to use an EZABL Pro, so it can have mesh bed leveling. I figured I'd make a copy of the Marlin folder I used when i upgraded, for a TFT touchscreen. Then I could make the changes needed, but still have the old file, in case I screwed something up (in many ways, I don't understand, exactly, what I'm doing when it comes to Marlin).
So, after making the proscribed changes I tried to verify and got a bunch of errors.

I opened the old file and verified it and got a bunch of errors on it as well! This is the file that I verified and uploaded to the printer last year, with no problems. I don't believe I have made any changes to this file. What can cause this?

Also, is there anywhere that I could learn how to understand the error messages and how to fix them?

1) stop using Arduino IDE, it cannot handle marlin anymore as it got to large. Use vscode and platformio [marlinfw.org]

2) there seems to be something wrong with your E0_AUTO_FAN_PIN definition in your Configuration_adv.h

Thank you, I will download & install them right now.

Quote
Dust
1) stop using Arduino IDE, it cannot handle marlin anymore as it got to large. Use vscode and platformio [marlinfw.org]

2) there seems to be something wrong with your E0_AUTO_FAN_PIN definition in your Configuration_adv.h

Using Vscode with PlatformIO worked! It compiled with no trouble.

Thank you Dust

Now on to the upload