Note that the the Java plugin and webstart was removed a long time ago.
I personally regret that the API was removed as it's a few classes and they are still used. Just search JApplet on Github. It's also possible to run applets in the modern browsers with WASM or in Java IDE's as plugin.
I can't answer for the File Pilot author but I've spent many years on writing a file manager.
* It's fun to write and to use. It's like craftmanship.
* Hopefully some companies/people will realize how many hours they waste using the default OS file manager
* It's less risky than developing a game full time (I think)
* Sure, I lost a lot of money to not having a normal job but my bills are low and my priority is more happiness
Better than asking what the money is for, even if the customer gives a reason like "buying a car", warn the customer that if someone on the phone or is unknown at your door asked you to do it urgently it's probably a scam even it they say they are from your bank/company/authorities.
For Linux, I'm using jpackage to package my Java software to .deb (x64 architecture) file. For all the other Linux variants, I've a .tgz file that contains the jar file, libraries and icons of the applications.
The problem I have with Linux is named at the end of the website: "Sharing your creation". It's pages and pages of documentation that is not relevant to the packaging of your application where you can spend hours of work without finding what you want of finding out that it doesn't work for you because for example it's not on GitHub.
Hopefully jpackage was able to fix it for the .deb format.
Instead of working on more documentation, working on better and easier to use packaging tool would help.
I don't think that what's friends are for (to test your app). Meaning, you'll need to go to a paying service, making it harder to justify afterwards to make your app free without ads or in-app purchase.
I personally regret that the API was removed as it's a few classes and they are still used. Just search JApplet on Github. It's also possible to run applets in the modern browsers with WASM or in Java IDE's as plugin.