The setup for Dragonflight is slightly different from Classic WoW. You no longer need to get the bite colour.
Just get the red colour of the fishing bobber and disable the "WOWClassic" option.
Set your World of Warcraft graphic settings to low.
Everything else is the same like fishing in Classic WoW.
More Tips you can finde here: https://wow-fishbot.com/en/blog/detail/sCategory/10/blogArticle/2