We are also hosted on a shared server using Moodle 3.3. Like you I would have liked teachers to annotate PDFs in the assignment module but our host will not install this feature on a shared server. I don't miss this feature nor did I hear any complains from other teachers. As we have a very tight budget for our DE site, I am glad that we are still hosted on a shared server with a timely and competent technical support. So you are not alone on a shared server without the annotation feature. But if you really want it, your host may have a plan that includes the installation of this feature.
With kind regards,