Johnson has repeatedly stated that Black Adam will face Superman. However, Henry Cavill's run as Superman has been in question for some time. Several of the original actors portraying Justice League members have been open about the possibility of being replaced. In addition to Ben Affleck, Henry Cavill is also very likely to lose his role as Superman.
Apparently, this doesn't bother Dwayne Johnson, who admitted in an interview with Total Film (via GamesRadar) that he doesn't care who plays Superman. So it doesn't seem like getting support from The Rock is a guarantee.
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Will Henry Cavill keep playing Superman?
All Dwayne Johnson wants is a Superman who can propel the DCEU forward.
To quote him:
A real fan who was frustrated with the original DC movies pushing them to greatness sounds excellent. Although many fans loved Henry Cavill as Superman, does that matter to The Rock? Yes, and no, he cares about having an actor who does it right rather than who does it.

He continued:
Cavill has stated that he's just waiting for a call to play Superman again, but if no one is calling, then that's pretty clear. Henry Cavill might not stay in the role long enough to be Superman again. After all this time, it is really looking like another Superman will fight Black Adam.
Would it matter if someone like Michael B. Jordan or Jon Hamm played Superman? What do you think?