While the nostalgia for .jar files is real, downloading software for older devices can be risky.
Searching for that keyword today is like searching for a phone booth. You won't find a working one, but the search itself tells a story.
If you have a (e.g., Nokia, Sony Ericsson, Samsung from ~2007-2011):
No one manufactures new phones with 240x320 Java support. The last Nokia S40 device was discontinued around 2014. Today, even $20 Android Go phones support 480x854 resolution and native YouTube Lite.