When still in the middle of teflilat amidah and the tsibur is reciting kedusha, one is supposed to be silent and listen. However, what the tsibur says is often not intelligible. Is it permissible to be meharher kadosh kadosh kadosh and baruch shem kevod malchuto?
If you cannot hear the chazan saying kadosh etc, then you are not yotza with what he is saying. In the case you may continue davening shemona esrei. If you specifically want to be meharher kadosh, you may, and it isn’t a hefsek, however you are not gaining anything by doing so because you are not yotza that way.
If you are at the end of the second bracha of shmona esrei, then you may say the kedusha together with the chazan.
O:CH 104-4, 109-2, M:B 104- 27, Poskim.