If you have ever mistakenly added a word to the Brave browser dictionary,
you need to manually edit the Custom Dictionary.txt file.
As of March 2020, the Brave UI lacks a feature to do this.
This will depend on your OS. Google for where this is on your OS.
The file on macOS is at: ~/Library/Application\ Support/BraveSoftware/Brave-Browser/Default/Custom\ Dictionary.txt.
Use your favorite text editor to edit and save the file.
As usual, with crappy Brave, it is buggy as can be. It works fine on Windows 10-11, macOS, but not on Ubuntu. Can edit the Custom Dictionary.txt file in /home/USERNAME/.config/BraveSoftware/Brave-Browser/Default and it shows up in the brave://settings/editDictionary GUI, but the red squiggles never go away on words in the Custom Dictionary.txt. There iOS Brave is extremely buggy and crashes often. Typical nowadays with Big Tech entry level cut and paste coders using GPT/CoPilot.
On MAC OS, update April 2024, they moved the location of the dictionary to:
~Library/Application Support/BraveSoftware/Brave-Browser/Default
When you right click and select "Add to Dictionary" in Brave, it creates a file "Custom Dictionary.txt" in the Default folder. I have edited that Custom Dictionary.txt, deleted, it done what I can think of to remove incorrectly added words. However, nothing has fully removed those words from the custom dictionary, that is, they are still incorrectly spelled, but not indicted with a red line.
This is the furthest I have gone, can anyone give an update how to reimplement the red lines on words that are accidentally-added to the dictionary?