Those spellcheckers don't seem to be able to offer suggestions with the remote hackmd notes. I'm not sure if this is easier to implement on their end or your end.
When I'm working in a local repo on my laptop VSCode offers suggestions no problem, but not with HackMD's remote notes.
When using the Spell Checking Extensions offered by vscdoe: https://github.com/streetsidesoftware/vscode-spell-checker
Those spellcheckers don't seem to be able to offer suggestions with the remote hackmd notes. I'm not sure if this is easier to implement on their end or your end.
When I'm working in a local repo on my laptop VSCode offers suggestions no problem, but not with HackMD's remote notes.