Reductio ad absurdum is similar to whataboutism, but it's not the same. Whataboutism is more like an abrupt detour off into a different issue to try to confuse

Reductio ad absurdum is similar to whataboutism, but it's not the same. Whataboutism is more like an abrupt detour off into a different issue to try to confuse the conversation or transform the topic of discussion into a referendum on the personal morals/motivations of the involved parties. The appeal to extremes does have to ask the question "what about x" but it's relevant because it's done to demonstrate the logical consequences of the other person's line of argument. It's not trying to deflect, it's getting to the heart of the issue.