BuildCraft version: 7.1.23
Forge version: 0.13.4.1614
Link to crash report or log:
Singleplayer or multiplayer: Singleplayer
Steps to reproduce: https://pastebin.com/7eQS74HR
Additional information: Crash in stable

it seems somehow the jar is containing the 1.12 api (ITooltipFlag did not exist back then), checking files

files all look fine, where did download the file from? it seems to not have been compiled correctly

can you re-download from the site (https://www.mod-buildcraft.com/pages/download.html) and try again?

i download from this official site