Students have always cheated, yes, but the barrier is UNBELIEVABLY low now. Take a picture, get the answer. This has never been a thing on such a large scale. No one knows how to deal with this.
In person testing is a solution for most issues, but not all. First off, class time is precious. I shouldn't have to waste incredibly valuable instruction time doing the actual test. We should be reviewing the test and learning things. Second, on-line classes are massive for many if not all schools. Requiring students to show up physically is both inconvenient, and (depending on which accrediting agency you are accredited by) not allowed.
It's not that simple. No problem of this scope will be simple.