According to documentation for popular versions like MrKinau's FishingBot and julianperrott's FishingFun :
: More complex bots (common in WoW versions) may read game memory to determine exactly when a fish has bitten. FishBot.zip
: Modern bots are often built to be compatible across multiple game versions (e.g., Minecraft 1.8 through 1.20+) and work in both offline and online modes. FishBot.zip
: Some versions use screen-scraping or pixel detection to "see" when the fishing bobber changes state. FishBot.zip