The backstory: Apple deprecated the QuickTime libraries in 2011 when they introduced AVFoundation on Mac OS X Lion, and they ended official support for QuickTime on Windows back in 2016.
Further, Apple announced in the summer of 2017 that the High Sierra (macOS 10.13) would be the last release of macOS to support 32-bit applications (such as QuickTime and the QuickTime frameworks). There has never been a 64-bit release of QuickTime, so there will be no way at all to use the QuickTime libraries on the next release of macOS.
Please note: this does not mean the QuickTime .MOV file format has been deprecated. We can all still use .MOV files, but developers will no longer be able to use the Apple QuickTime libraries for building apps that read, write, encode and decode them.
Since there's an entire industry relying on QuickTime, developers including Adobe have been writing their own QuickTime library replacements. Adobe's is called MediaCore. Adobe has written direct support for a number of QuickTime codecs [link] that are commonly used in production into the so-called DVA apps (Ae, Pr, Au, and AME).
Unfortunately, JPEG2000 is not one of them. As a workaround, you can download the previous version of After Effects (Ae CC 2018 v15.0.1 still supports 32-bit QuickTime codecs), or you can download the previous version of Adobe Media Encoder and use it to transcode your legacy media to one of the supported formats.