How to run a jar file that used to be run with appletviewer under macOS Monterey?

Solution 1:

That's not enough; applets have some frameworky bits that the app itself simply does not have, but needs to run. You either need a browser, or an app called appletviewer that used to ship with JDKs but probably no longer does.

Find the oldest JRE/JDK you can find out there and pray that it includes an app called appletviewer. If you can't find one, then you must have the sources to this app and know a little bit of java and you can fix this (pretty much make a JPanel in a JFrame and render the applet in that; presumably the applet doesn't interact with browser specific API, as very few applets ever did that).

If you don't have that skillset I'm not aware of any automated way to do this.

NB: There is no main class; the applet runner itself is the main class. The first code that runs from that actual app is Texture.class – it doesn't have a main method, nothing in that jar would.