Terminé con esto, resuelve el caso.

  with calendar as
  ( select cast('2005-01-01' as date) as [Date], 2022 as [Year], 1 as [Month], 1 
  as [Day]
  union all
  select dateadd(day,1,[Date]), DATEPART(year,dateadd(day,1,[Date])), 
  DATEPART(MONTH,dateadd(day,1,[Date])), DATEPART(DAY,dateadd(day,1,[Date])) 
  from calendar
  where [Date] <= '2030-12-31'
  )

  select c.*,
  CASE c.month when 1 then SUBSTRING(t.TFACS_MON01,c.Day,1)
                                                        when 2 then 
  SUBSTRING(t.TFACS_MON02,c.Day,1)
                                                        when 3 then 
  SUBSTRING(t.TFACS_MON03,c.Day,1)
                                                        when 4 then 
  SUBSTRING(t.TFACS_MON04,c.Day,1)
                                                        when 5 then 
  SUBSTRING(t.TFACS_MON05,c.Day,1)
                                                        when 6 then 
  SUBSTRING(t.TFACS_MON06,c.Day,1)
                                                        when 7 then 
  SUBSTRING(t.TFACS_MON07,c.Day,1)
                                                        when 8 then 
  SUBSTRING(t.TFACS_MON08,c.Day,1)
                                                        when 9 then 
  SUBSTRING(t.TFACS_MON09,c.Day,1)
                                                        when 10 then 
  SUBSTRING(t.TFACS_MON10,c.Day,1)
                                                        when 11 then 
  SUBSTRING(t.TFACS_MON11,c.Day,1)
                                                        when 12 then 
  SUBSTRING(t.TFACS_MON12,c.Day,1) 
                    END as WorkDay

  from calendar c
  join [TFACS] t on t.TFACS_JAHR = c.Year

  ORDER BY Date

  OPTION(MAXRECURSION 30000)