Arduino IDE will no longer start

I have been using the Arduino IDE on my Raspberry Pi 3+ for over three years. I had updated several times and was running 1.8.10 when this phenomenon first occurred yesterday. The IDE will no longer start. I get the initial splash page and at the bottom it says "initializing packages..." but after a few seconds it quits and doesn't complete the startup, it never shows "Preparing Boards...", just dies.
Today I attempted to install 1.8.12, but after install, it too fails to run in the same manner.

I read the post by pert and deleted the mentioned files and cache dir, but still no joy.

I have the 1.8.5 IDE running on another pi, and it is still working fine, so I'm afraid to update that one. Help!

(deleted)