Monthly workload summing each phase from each project

Thanks vojtechsima,

I spent few more hours on it this morning.

Finaly, I tried to mimic your code in adanced editor until your step "Removed Duplicates1":

    // Ajout de la colonne "key"
   key = Table.AddColumn(#"Changed Type", "key", each Text.Combine( {Text.From([ProjectId]), [Projects.ProjectOwnerName], [Project Phase] }), type text),
    
    startDate = ()=>
    let
    #"Sorted Rows" = Table.Sort(Source,{{"TaskBaselines.TaskBaselineStartDate", Order.Ascending}}),
    Buffer = Table.Buffer(#"Sorted Rows"),
    #"Removed Duplicates" = Table.Distinct(Buffer, {"key"})
    in
    #"Removed Duplicates",
    
    endDate = ()=>
    let
    desc = Table.Sort(key,{{"TaskBaselines.TaskBaselineFinishDate", Order.Descending}}),
    Buffer = Table.Buffer(desc),
    #"Removed Duplicates" = Table.Distinct(Buffer, {"key"})
    in
    #"Removed Duplicates",
    startDateColumn = Table.AddJoinColumn(key, "key", startDate(), "key", "earliestStartDate"),
    expandColumnStart = Table.ExpandTableColumn(startDateColumn, "earliestStartDate", {"TaskBaselines.TaskBaselineStartDate"}, {"earliestStartDate"}),
    endDateColumn = Table.AddJoinColumn(expandColumnStart, "key", endDate(), "key", "latestDueDate"),
    expandColumnEnd = Table.ExpandTableColumn(endDateColumn, "latestDueDate", {"TaskBaselines.TaskBaselineFinishDate"}, {"latestDueDate"}),
    #"Removed Duplicates1" = Table.Distinct(expandColumnEnd, {"key", "earliestStartDate", "latestDueDate"})
in
    #"Removed Duplicates1"

But I face an error I was not able to solve:

Any idea on what is wrong?

Fab