Specific GA4 custom event calculated metric

How can I get a calculated metric that counts the number of sessions in which a specific GA4 custom event was fired?
I need that to create a table with 3 columns:

  • sessions count
  • count of sessions in which a specific custom event was fired
  • session conversion rate (e.g. second column / first column * 100)
    In the rows, every campaign that I run.

Thank you!