I have a question about in-text citations. I have read different answers and want to be sure about it: when I paraphrase a text from paper A, I should cite the author; if there is a reference in the text which is the author of the paper B, paper C and so on, should I also cite them in my text? Is there any other way besides using "as cited in"? For example, in paper A there are multiple sources that the author refers to like ,,  in the part that I want to paraphrase. Should I cite them all?
This question is a bit vague, but if we assume you are trying to publish a paper in a peer-reviewed journal you can follow the general rule of cite any ideas that are not your own and try to cite them at the source. Best practice is to find the paper the idea originally comes from but that is not always necessary. Obviously if we did this all the time we would have unwieldy reference lists. For example, a review is appropriate to cite by itself, rather than citing all of the papers it draws from. There is an argument to be made for including direct citations to important papers from that review, but I doubt anyone would fault you for just citing the review when discussing general background information or the state of the field. On the other hand, it would not be appropriate to only cite an unrelated experimental paper that contains a relevant citation in the introduction.
This is based on my experience and can be very subjective. It also assumes you are holding yourself/being held to a relatively high standard. Even if this is not the case, I think that it is still applicable as a guideline. Ultimately you need to decide what papers are worth citing.
A side note, I'm note sure you should be "paraphrasing" anything to the extent that you even need to ask this question. There is a difference between synthesizing information and including it in your paper (with appropriate citation) and lifting entire sections from something you've read. Tread lightly here.