So, you can say, "I eat fish" to mean that you habitually eat fish, or "I'm eating fish" to say that you are doing it now. But if you say, "I can't eat this", it's possible that you mean either 'habitually' or 'now'.
Some modals can be used in the continuous tense with 'be'.
"I could be studying [now] instead of answering questions here"
"I would be riding my motorbike [now] if it wasn't raining."
Student or Learner