It’s almost certain.
Here’s Chris at 38 in Thor Love and Thunder.
And here he is in Heart of the Sea in 2015.
Testosterone begins to decline steadily starting around age 30, and Chris doesn’t appear to have a natural bodybuilder build, based on his actual height and his height in the aforementioned movie. Sure, bodybuilders can be his size, but it’s certainly not the norm.
Achieving such musculature and volume, even at 6’3 (1m90), is almost impossible without steroids, even with fantastic genes, and especially at this age.
With hundreds of millions, if not over a billion dollars or more at stake for Disney, it should come as no surprise that Chris is on steroids. Plus, you know, his box office success is partially based on his body, so taking steroids is a relatively minor risk, both legally and physically, to remain a box office star.
Edit: Some people take this as a dig at Chris or an insinuation that he didn’t work hard because of the steroids. The opposite is true. Chris worked much harder than anyone not on steroids because that is precisely what steroids allow the user to do, train and recover much faster than without steroids, which also means much more time in the gym.