Spell checker does not work in Gemini or Substack, and I have followed all troubleshooting interventions I can find

Spellchecker does not function, and in my most important projects, Gemini and Substack, no spell checking takes place, I have to switch to Chrome of all things...here in this field spell-checking is taking place...why? I have spent much time researching this issue, made all the intervention recommended, nothing works, and the failure is 'selective', works on many things, fails on important production browser interfacing. I value being Chrome-free, please help me solve this issue