The more solo mining, the better it is for the network.
Correct me If i am wrong?
Decentralization, in theory, yes. In practice the ability to mine in pools encourages more small miners to participate so I'd say that outweighs the negligible chance that e.g. pools might try to cut the branch they're sitting on by colluding or otherwise trying to harm the network.
What I mean is: if I mine with 100 S19Pro, each one of them can be possibly considered by them a different miner?
Or maybe it’s my decision if enter with one account with 100 miners, or 100 with a single one?
You can choose to group your miners however you want. That's no different from mining in a regular pool or mining "real" solo completely on your own (without ck). However the pool operator can see your IP so they would have some idea which miners are related.