The document formatting features of BrailleExtender such as bold, underline italic and so on, are also not working with NVDA 2026.1 and I think you can not just define those 3 simple modes anymore like enabled, disabled and like speech, because in speech the NVAccess itself made a different modes which can be toggled such as speak font attributes, braille font attributes speak and braille and off.
I can offer a different solution instead. You can completely uncouple the presentation of those formatting elements from speech and make them only enabled or disabled in Braille. Then you can also add an option to make a shortcut keys to briefly enable or disable any of those formatting elements in braille, exactly as you can do this for speech under the formatting options in the input gestures dialog of NVDA for speech.