I currently have a sketch fully working on an ESP8266 board. This has been running for almost 4 years
I have made a minor change to the sketch and now it wont compile.
I recently had a similar issue with an ESP32 and somebody on this forum got me to make some changes under the 'tools' menu in the Arduino IDE (Partition size - Hugh App) and it all worked again.
Is there a similar process that I need to do for the ESP8266 to 'roll it back' to when it used to compile?
So that we can help you, please inform the version of your IDE and post,
(using the recommended tags), your complete code.
Those 'minor' changes kept me employed at 6 figures for decades. Post the code in code tags and if you can show (in comments the old code as well)
bro give more details
I have literally just changed an API version number from 2.5 to 3.0
I am using IDE version 2.3.3
I have the old version 1.8.19 on an old laptop. I will see if this makes any difference
what if you go back to the ESP8266 original code will it compile?
post code and the compiler/linker messages (as text not a screen image)
I have rolled back several libraries that the sketch uses and also the Node MCU 1.0 (ESP-12E) board
and now I have got it compiling and running again.
I have a strange graphic appearing on my TFT so I will now mess with the TFT_eSPI library and settings to see if I can iron that one out.
Going forward, I am going to add library and board version numbers to each sketch so that if update anything in future I can always roll back.
SORTED 
The TFT_eSPI.h library uses a User_Setup.h file that just needed tweaking (output pin numbers)
No in fact it uses the same core & library structure, but in many cases by changing the library header file name it will work.
