Autocomplete popup when adding a link using [[ ]] never appears

Hi, I don't suppose anyone can help me! All of a sudden the autocomplete box won't appear when attempting to enter a link - I'll type the brackets [[ and nothing happens. I was using the beta and have tried reinstalling but no luck. I've also uninstalled the beta and reinstalled version 1.89 but that seems to now have the same problem too! Any ideas? I'm on macOS Big Sur.