Also a lot less flopping on the ground in fake agony. With no crowd to play to, players fall over and then get back up again. It's very refreshing to watch.
For some (and I mean in no uncertain terms, for black players and those from other minorities), it's probably a godsend, and that sense of 'relief' probably does have a measurable outcome (i.e. some players raising their standards, and others doing likewise to follow them).
OPTA and their like measure a lot of data points. So this hypothesis could probably be proved. Passing percentages, XG and assist rates for example, but I'd reckon individual running distances will be a particularly interesting metric to explore.
Any of those stats could go up or down for all players, but I do suspect there will be observable changes, because of these new playing conditions.
It's very easy to trip when sprinting at full speed while concentrating on a single object. The slightest external force will put you on the ground very quickly.
Rugby, Gridiron and Ice Hockey players will also know that, but frequent falls under pressure are expected by the rules. In soccer, it's a lot more subtle (shirt pulling, various rules around obstruction, the height at which you keep your hands... all sorts). There's plenty of opportunity fool a referee, so you will instinctively try to do so. Especially if your style of play generally draws opposing players into fouling you regularly already.
I'd say that the introduction of video referees (VAR) are probably more effective in stopping that kind of behaviour, than empty stadiums. But you'd never know.