"for the main question and not to other questions as I was able before."
I guess you mean: "for the main question and not to other answers as I was able before."
This is still possible.
By design the comment can only be converted to posts (Questions or answers) that were posted before the comment was posted.
Take another question with answers, and an answer that were posted after the other answers. You will be able to convert it and choose its destination post.
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April 20, 2021: Q2A 1.8.6 released!