gws - Your question is "precisely" what I was trying to find out when I realized it wasn't working.
As far as I know, there was a Lighthouse update. But, one of the people who responded here stated that he used a UNIX server by installing Lighthouse and it worked.
HOWEVER...he posted a few days later to say...it too no longer works. That tells me the version of Lighthouse he installed locally was a version "prior" to the updated that we have all tried now and cannot get to work with Joomla - any version - without disabling part of Joomla.
"I" still believe that it's Lighthouse...not Joomla.
I have tested all of my sites, even those I use for staging only. They "all" worked perfectly until the day before I posted.
I purposely only updated a couple to see if it made a difference. It did not. Joomla 4.3.3 did not work when I posted, nor did 4.4.0
And, I have one site that I use for staging and immediately after I updated to 4.4 there was another release to 5. But it failed too.
I've also continued to test almost daily and there is no change.
The Joomla developers moved this thread away from where I created the thread, saying it's a problem with Joomla. I can imagine they are scratching their heads now because no matter what they do, they can't get Joomla to work with Lighthouse either.
The only thing allowing Joomla to run Lighthouse is if you disable the "cross origin" plugin. I did that on a couple of sites, different versions, and Lighthouse worked.
But I'm one of those that does not take kindly to disabling something that has worked fine for years.
The bottom line is, "I" still blame Lighthouse for the last update they made which, for whatever reason, singles out Joomla sites - nothing else.
There is nothing I can imagine that would cause Joomla to "suddenly", without any sort of update, not work with Lighthouse.