Are retirees subject to UCMJ?

Super rare. The only case I know of is a retiree in Iwakuni Japan allegedly committed a heinous sex crime. Besides facing the Japanese judicial system he was reactivated for a court martial & booted out with a dishonorable discharge. Then transferred to Japanese custody.
https://www.military.com/daily-news/2019/02/22/supreme-court-retirees-can-be-court-martialed-crimes-committed-after-service.html

Yes, retirees are subject to the UCMJ. However, most of the time crimes are referred to the state or federal government rather than the UCMJ.

Does this apply to ETS not retirement as well? I understand the retirement aspect of this, but as the article states you have to be receiving pay if you don't as ETS status does that limit them?

Last year the U. S. Supreme Court refused to hear the appeal of the conviction of a retired Marine who raped a sailor in Japan. MilitaryTimes.com article. Military retirees can still be court-martialed, Supreme Court affirms

There was a case I read about where on appeal, the service member was subject. The service member was retired from active duty. Reserve component retirees aren't in jeopardy of UCMJ after retirement. The only reason I can think of is the pay status and Article 2.

I feel if retirees can be convicted in "retirement", I feel that they should be promoted in retirement. Example of this, is the Tuskgee Airman from Colonel to B. General.

Does this also mean we are protected by the Soldiers and Sailors Civil Relief act if we so choose to be? You have to look at this from all angles, not just the one beneficial to you. In this case law enforcement and prosecution.

I can't of any reason except classified info is given out.By a officer.Other wise it would be very rare

A retired first class petty officer was brought back to active duty after being charged with child molestation of the young girl who lived across the street from us (~1992)...found out when interviewed that he had also molested our child...yes he did go to court martial, but we left before results

Yes. As much as I disagree with it, all retirees AND those receiving VA disability are subject to UCMJ until they stop receiving said compensation. A Marine was recently dealt with thusly for rape in Japan. There are more cases than I'd like to think. ANY UCMJ violation can get you, but they normally won't waste time unless it's a major violation or a high profile/international one.