[error] thrown Runner: not possible: javax.script.ScriptException: ReferenceError: "find" is not defined in nashorn:mozilla_compat.js at line number 69

Use 2.0.0 and see:
https://github.com/RaiMan/SikuliX1/wiki/How-to-use-Launchpad-downloads

... or are you really trying to run scripts written in JavaScript?

java -version

openjdk version "1.8.0_212-8u"
OpenJDK Runtime Environment (build 1.8.0_212-8u-04)
OpenJDK 64-Bit Server VM (build 25.212-b04, mixed mode)

I just tried to run simple 4 liner script using IDE to check if it's worth to invest in it (automating RDP app)

... ok, but you have to follow the steps mentioned in the getting started information

I have on my windows path set up with all mentioned JDK/jython 2.7.1/jruby - I can start those without any issue.

I'm not sure what else is missing based on description here:
http://sikulix.com/quickstart/

I'm using windows10 64 bit

... ok, might be, but having Jython or JRuby on windows path is not the requirement, but what is said on https://raiman.github.io/SikuliX1/downloads.html in the section:
Needed for scripting support in the IDE and running scripts from commandline

... but the idea of using a Jython or JRuby from windows path is not that bad (I will register an enhancement for that)

... to follow up:
https://github.com/RaiMan/SikuliX1/issues/214

So I downloaded it because I thought that it might be a needed dependency as msg was thrown at IDE startup.
Still I can't find anything that I might be missing that would cause such issue.

Is the Open JDK relevant?
Or maybe some privileges as I'm using it without any admin role.

again:
the downloaded Jython jar must be in the same folder as sikulix.jar (as said in the mentioned link).