There are two questions here:
I am wondering is there a separate SE aimed at experimental physics
No, and in my opinion there shouldn't be. The most important asset of this website is the set of users, because they create the content. As a user and an experimental physicist, I want all of the users looking at my questions. In my daily work as an experimental physicist, I benefit enormously by intimate collaboration with theorists. They notice important features in data, suggest good experiments, explain observed data, and provide useful calculations related to our experiments. Splitting the users seems unwise, in my opinion.
how come there is so little experimental physics being asked here?
I think there are two reasons. First, there certainly was a bias against experiment questions here, and there's some recorded history on that issue. Once upon a time in 2014, I asked a question about lab equipment which attracted a number of close votes; certain users (who I surmise do not understand the nature of experimental physics), voted to close as "off-topic". The discussion arising from that (and other) incident lead to this meta post and its accepted and most-upvoted answer, which in my opinion suggests that questions of the type that I asked should be welcome here.
Now, has anything changed, i.e. are we better about allowing experimental physics questions to live here? My impression is that yes, things have changed. However, perhaps someone could run queries with the various experimental physics tags to see if we've actually gotten better.
Of course, I've only discussed whether or not the situation surrounding questions has improved. A functional Q&A site also needs answers. I can't say whether or not that situation has changed.
Second, I think the most important factor is that *experimental physics is less well represented in written material than is theory across all forms of written information.experimental physics is less well represented in written material than is theory across all forms of written information. In other words, if there's less experiment than theory on this site, it's probably because there's less experiment than theory at all in any written format. When you were a student, were you ever assigned to read a book on experimental physics [1]? In the highest impact physics magazines (Nature and Science) what's the representation of works focused on experiment? Experimental results are well received, but the techniques and engineering (the kinds of stuff I'd expect to be well served by Q&A) are not. Throughout my career, referee feedback on papers has pushed details on the experiment itself into the "supplementary information" section of the paper (which is not even peer reviewed!) [2]. When I review papers, I regularly have to push authors to include relevant details of the experiment into the main text, even when those details are critical to the message of the paper. I speculate, therefore, that the relatively low fraction of experiment-oriented material on this site correlates with the relatively low fraction of experiment-oriented material in physics literature at large.
P.S. I wrote this answer attempting to address the actual questions in the main post, and I wonder if those are the questions the author really wanted to address. An obvious related question could be "how can we improve this site's accessibility where experimental physics is concerned?"
[1] I wasn't. In fact my physics degree didn't even require basic electronics or even computer programming. It was very focused on theory.
[2] See for example the enormous supplement of the paper on quantum supremacy.