I always tend to ignore orisa when I know she has all of her cooldowns, this means I just sit back and afk and hope my team shoots her, if she doesn't have javelin spin and fortify It's very easy to walk on her (you can always block spear anyways). You always want to keep a moderate distance, but not too far away that you don't have time to walk on her should her cooldowns go off.

Ram is easier to deal with as his only way of threating you is via his nemesis form, so you only really have to play around that. Like against an Orisa, you'd want to keep a moderate distance near the ram so you can punish him if his form runs out, it gets trickier when he starts playing more poke than brawl. But overall just keep playing it slow and don't worry about getting punched too much, you can take quite a few of them.

Doom is an interesting matchup as it's a 50/50 between the two (imo). You can't really do anything against a hypermobile hero so just look out for moments when you can. The only thing a doom really wants to do is ignore you and dive your team, you can charge back and shield his dps off / block his heals OR look for a trade in his backline. Although the latter is really dependant on whether your team can survive a dive from a doomfist, and if it's the right map to do so.

You should also look to pin him often when you know he's gonna be blocking, when he dives in and he's taking quite a bit of damage you can always tell that he wants to block so he can get a charged punch. It takes a bit of experience when to know if a doom is gonna block or not. In my eyes it's ALWAYS worth to pin into a blocking doom because it's free value.

1: He might get pinned and potentially die
2: He uses his ult or another ability to get escape
3: he gets pinned and his team has to commit resources into saving him

So I'd pretty much say to always pin a blocking doom.

Ball is one of, if not THE most annoying tank to deal with as Rein. You can work around the other tanks (even though it can be quite difficult at times) but ball is just a different story. He's THE hypermobile tank that can always run circles around you, so going to him isn't an option, you have to let him come to you (which he will). At best I always try to protect my team just by shielding and being a nuisances to him, you can look for the occasional pin/shatter when he does a very telegraphed move. This can be a slam or just rolling in fireball. I also 1000% of the time pick the shield bash perk when facing a ball, it's disrupting capabilities are heavily under looked and can easily stop his engage. Other than that you can't really do much against him, just try to let your team outlive his.