Messi never ran much.
Here's for instance an article from 2014 about a game in which he ran 6.8 km. His season average in 2014 (8.2) was below the distance covered against City (8.3). It's always been a stick to beat him with when his teams lost. There were always many arguments that defended him,
this article provides quite a good overview. Some of them: He doesn't cover large distances but he makes more fast runs and sprints than most. Or that he does it to get into better positions and that it is actually anticipation. Many players have to learn to run less during their developing years to become more effective, it's actually quite a common theme.
In summary, the line of argument was always that Messi moved less but still got into enough positions: His pressing stats were good, he got into enoug goal scoring positions and so forth. Currently neither of this is the case. His pressures per game dropped significantly and he also gets on the ball less frequently in dangerous areas. But this doesn't necessarily have to do with his work rate, it might also have to do with the team shape, tactic, cohesion etc. Of course it is harder for him to "get a grip" on an opponent player carrying the ball or intercepting a pass when there are two other players on the pitch who do as few as him or even less in Mbappe's case.
I guess the stats that would really help to paint a clearer picture are fast runs, sprints, etc. and compare them to previous seasons. I doubt that his stats in these areas are much worse than they used to be because his distance covered remained largely the same throughout all those years. So if he reduced the intensity, this would mean that he would have moved more by walking/jogging etc. and that doesn't seem to be the case.