How do I access "Comparison View (X|Y)" in the latest version of Lightroom CC? It was previously found as one of the view options in older versions of Lightroom CC.
That feature has not (as yet) been implemented in the cloud-based version of Lightroom CC. It is a new program that is being developed completely independently from what you referred to as the "older" versions of Lightroom.
You need Lightroom Classic. Adobe made the very unfortunate choice to reuse the Lightroom CC name for a completely new program which is basically a port of the mobile version of Lightroom to the desktop. It renamed what used to be called Lightroom CC to Lightroom Classic. Adobe is very slowly adding features to Lightroom CC that are present in Classic so in a few years we might have X/Y view in CC but currently you can only get it in Classic.