What kind of class/course is COMM 121 (Interpersonal Communication) that's taught at a community college?

Every class is different at every school.  So no one really knows how that course is taught at that school, and how easy or hard it might be.  

Most universities do require a "public speaking" course, which is usually offered through communications.  This is probably that course.  It generally involves preparing and presenting various types of speeches.  I don't know how they plan to structure that online.  Our university has the students present over Zoom.  

You should not need this course to transfer.  But you will probably need this or a similar course to graduate. 

There are no requirements from any community college for you to transfer to a 4 yr university.  You can transfer at any time.  

Communication classes are total fluff.  You'll have to make a couple speaches or presentations.  Some people would get stage fright doing that in front of the class, but that goes away doing it online.  You'll probably just need to video yourself giving a presentation.

I agree with Gypsyfish.

You'll have some readings, maybe from a textbook and maybe articles, about how people communicate with each other.  There will almost certainly be projects you'll do with a few classmates focusing on small group communications.  You'll also almost certainly have to prepare a talk for the entire class.  Since it will be online, you'll be using zoom or a similar platform quite a lot.

It is typically not a particularly difficult class.  People who are shy or have social phobias may worry about it, but they too get through the class.

There will be some theory- some reading about what research has shown about communication. Typically, a class like this would require some class presentations, to build your skills and confidence. My guess is that an online version will have you record some presentations, or do them on Zoom. That can be more or less stressful for you depending on how you feel about seeing yourself on a screen. But it's important to do this. There's no job worth having that doesn't include some public speaking, to clients, in meetings, etc.