As I understand it, some nouns have a special する-verb status that allows them to be used with する (or します) without を. Nouns that don't have this status have to have を, but nouns with this status can be used with or without を.

If you look in a dictionary, it'll usually say if a noun is a する-verb.

I think you mean を plus します, right?

I struggle with that too: sometimes を is there (べんきょうをします), sometimes it isn't (テニスします). I asked this same question about 何をしますか and got some helpful replies but haven't internalized them enough to be able to repeat them. I'll see if I can dig up the link.

Here it is: https://www.duolingo.com/comment/23027831

を、し do not usually go together. I suggest that you give some examples which you have find confusing for more relevant answers.

In that case I would reply in the older thread.