I last paid active attention to this in mid-2017. At that time, Google mostly, eventually executed JavaScript, but it would often be weeks after initial indexing that any JavaScript execution happened; and there were rumours but scarcely more that Bing could execute JavaScript; and I know of no other engine doing any JavaScript. By mid-2018, Bing definitely sometimes did some JavaScript execution (see https://www.screamingfrog.co.uk/bing-javascript/). It’s probable things have become a bit more consistent by now, but actually loading pages realistically is so much more expensive than just parsing the initial serialised HTML that I think you can reasonably expect JavaScript-execution to be less consistent and reliable as they will very probably continue to prefer to avoid loading things that way if it’s not obviously required.