it is crucial

Is thie second alternative correct?:‘He really must attend the meeting.’-‘It is crucial to attend the meeting.’
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He really must attend the meeting.
It is crucial that he attends the meeting.

The second alternative is grammatically correct, but it doesn’t apply just to him. It applies to people in general.

“It is crucial that he attend[color=red]s the meeting,” is not correct, because it means that he already attends some repeating meeting regularly and the fact that he does so is crucial. If you are talking about a meeting that hasn’t taken place yet, you need to use the subjunctive and say, “It is crucial that he attend the meeting.”

Look at the difference:

Present simple: “It is important that he is at the meeting.”
= He is here now, and that is important.

Present subjunctive: “It is important that he be at the meeting.”
= There will be a meeting later, and his presence there will be important (if he comes).