Any suggestion on a suppressor that might work on a piston 16" AR 5.56 and also a 5.7 pistol? Both threaded 1/2 x 28. Pistol has a red dot. Mostly concerned about diameter so sight is not totally blocked. A pistol 5.7 that could withstand 5.56 would be okay as I use ear protection. Not sure if such an animal exists as I am new to supressors.

Maybe a Griffin Optimus Micro.

^^^ That.

I'm intending to get an Optimus Micro as a dedicated can for a PS90 SBR.

First ANY 5.56 can will allow you to shoot 5.7. But all of them will suck from the point of view of size and weight on a pistol (I am assuming the pistol doesn't need a booster as that complicates matters a lot). And any can that seems ok for size and weight on a 5.7 pistol will suck in the 5.56 suppression situation.
What diameter would be ok? Mostly anything will not block the sights with a red dot on any pistol I own.
lastly 5.7 is very lightweight in the suppressor situation and many rimfire cans are happy with it. I use a DA. Those will be light and small and totally usable. None of them do great at least with commercial ammo which is not subsonic (why FN won't give us the subsonic rounds sucks) but at least you won't have a huge 5.56 thing hanging off the gun.
Anything that can take a steady diet of 5.56 that is light and small will probably have sucky performance on 5.56.
Mostly what I would suggest is that this is a huge gap for one suppressor to be optimal. So maybe get two.

Neither the FN FiveseveN nor the Ruger 57 use a booster piston. They are delayed blowback pistols and need either direct thread or a fixed barrel spacer if you do use a can that has a booster. Don’t know if that’s the same for any other 5.7 pistols.

I understand regarding the smaller can not suppressing 5.56 very well and am willing to accept the shortcomings in that area. Being supersonic 5.56 has built in limitations regarding sound control. I guess I should have made it more clear that the primary use was on the pistol but secondary on the rifle. I do have a 30 cal can that I can use on the AR if I need further suppression.

Then the Optimus Micro is probably your best option. I don’t know of any other small diameter (~ 1.1”) can that is also rated for 5.56. Most 5.56 cans are at least 1.5” in diameter.