What is the ruling on saying: "O Allah, whoever intends us harm, turn their plot against themself..." in a general form, and when should it be said, and is it better to abandon it, and is it permissible to continue saying it during times of tribulation and when people's true nature is revealed?

The aforementioned supplication is good and there is no objection to it. It is among the unrestricted supplications, but it is not one of the morning and evening remembrances, so it should not be believed to have any special merit at this particular time. It is important to note the caution against entertaining ill thoughts about Muslims and accusing them without clear evidence, in accordance with His, the Almighty's, saying: {And those who harm believing men and believing women for [something] other than what they have earned have certainly borne a slander and a manifest sin}.