Does this sound natural? 😁
consider that the big problem with online class is that students don't learn well this way because people are bound to need to connect with one another

See a translation

Good job! But this sentence is a little to long. A better way to say it would be “consider the big problem with online class: students don’t learn well because people need to physically connect with one another.”
A colon “:” is best used in this case because it comes before an explanation. Think of it like “consider the big problem with online class:” is the thought, and “students don’t learn well because people need to physically connect with one another” is the explanation of that thought. Both sides of the “:” can be their own sentence, that’s how you know you can use a colon!
I hope this helps!