I can only say that on my last 5 intra European flights (over the last three months, even before Omicron) I was pinged by T&T exactly 5 times two days later, so I would say the chance to have someone on board who is positive is relatively high.

Just a data point - of course would not show a positive test on arrival if just exposed in the plane.

I would be more concerned about a positive pre departure test (but I assume they won't be required anymore rather soon).