Java Update past 17 - How To?

Hello again, I’m getting my server up and running again so my Nephew can have a safe place to play with his friends.
I tried to make a new server (in the webUI) and wanted to try 1.20.6
After doing the regular stuff I accepted EULA and tried to start the server but nothing is happening.
I tried to download and install a newer version of Java (25 I believe?) but it wasn’t working properly… then the WebUI broke.
I had to backup all my server files using Filezilla then Nuked & Paved the machine with the newest ISO of Turnkey I could find.
All my old worlds are still functional (running java 17) but I still cannot get the 1.20.6 world to even start loading, no console log, WebUI notifications show “bork_town Start:success” but the green start button doesn’t lighten (as if pressed down).

Any ideas for how to update java easily? I found this forum post, but it only tells how to update TO Java 16. Is there a newer set of commands to use? I would like to not try the way I did in the beginning - see linked post (I followed the steps but changed the new java version to 25 after finding the java downloads webpage).

Any help is appreciated.

I looked around other posts and found This One.

Is this the proper way to go about updating java to 21?