just check the cast list. Robert Downey Jr currently not there.

Tony Stark and Iron Man are also currently absent.

I don't think its too hard to find an actor with very good voice impressions to RDJ

Evans and Downey are unlikely to return despite their characters likely appearing.

Also, the 23 episodes thing hasn't been confirmed and is unlikely. Feige made a vague statement that was just interpreted by some as 23 episodes.

Considering they brought back the other actors, I doubt they would recast someone’s voice just for this show. I don’t think they will have him in here, but he could be a surprise saved for later.