Change data set structure, unsure how to transform this

AllanT1495 

That appear to be a classic 'unpivot' operation and the best point at which to apply it is often within PowerQuery before the data is ever loaded to Excel.  Now however, Excel itself is reasonably capable when it comes to such restructuring (normalisation) processes.  The basic function to apply is TOCOL

= TOCOL(date)

but, assuming you also want the row and column headers to appear, this becomes

= LET(
    p, IF(date, project),
    g, IF(date, gate),
    HSTACK(TOCOL(p), TOCOL(g), TOCOL(date))
  )

where the formula assumed 'date' to be datevalues and contain no blanks.  If there are blanks, the next step is

= LET(
    p, IF(date, project, NA()),
    g, IF(date, gate, NA()),
    HSTACK(TOCOL(p,3), TOCOL(g,3), TOCOL(date,1))
  )

As an aside, to reverse the process using the insider version of 365

= LET(
    project, CHOOSECOLS(unpivotted, 1),
    gate,    CHOOSECOLS(unpivotted, 2),
    date,    CHOOSECOLS(unpivotted, 3),
    PIVOTBY(project, gate, date, MAX, , 0, , 0)
  )