In my experience the committee exists to gather/synthesize the letters you already have. I don't know where you are in your schooling ie. freshman, soph, etc, but in the future if classes continue online then you need to reach out to your professor and say - I want to do graduate school, I need an LOR - how can I demonstrate to you I deserve a letter.
The simple truth is - if you take a class, never speak to the professor, never interact with the professor then what do they really have to offer you besides your grade. "This is a student. They earned a 89 with a class average of 79 and a standard deviation of 5. I have never spoken to them." I don't disagree that this will be more difficult than if you were able to speak to them face to face.
When I went to school I thought the best letter chances were organic chemistry and upper level science. The classes had labs, they were hard, lots of office hours available to discuss - the kind of opportunities to interact and show your interest.
Good luck.