It's kinda silly, but I like "frhed" for Windows. It's a small fast hex editor. I tried more advanced editors but found myself going back to frhed because it opens instantly and never complains, it just opens any file and lets me get to work.

https://sourceforge.net/projects/frhed/

On a similar note I also use Notepad2 which hasn't been updated in years, but is a no-BS upgrade from Notepad that also will open just about anything very quickly. I use it more than Notepad++ because of the balance between simplicity and function, and it never gives me popups to update.

https://www.flos-freeware.ch/notepad2.html