Week on Week Actual Variance + with Forecast Variance

pupadhya , Create a new table with distinct of this column( If there is year take that)

Distinct(Table[Day])

Or have table with week year

Create a rank of Day oe week year in new table , new column

Week Rank = RANKX(all('Date'),'Date'[Day],,ASC,Dense)

or

Week Rank = RANKX(all('Date'),'Date'[Year Week],,ASC,Dense) //YYYYWW format

then try measures  like
This Week = CALCULATE(sum('Table'[Qty]), FILTER(ALL('Date'),'Date'[Week Rank]=max('Date'[Week Rank])))
Last Week = CALCULATE(sum('Table'[Qty]), FILTER(ALL('Date'),'Date'[Week Rank]=max('Date'[Week Rank])-1))

Power BI — Week on Week and WTD
https://medium.com/@amitchandak.1978/power-bi-wtd-questions-time-intelligence-4-5-98c30fab69d3
https://community.powerbi.com/t5/Community-Blog/Week-Is-Not-So-Weak-WTD-Last-WTD-and-This-Week-vs-Last-Week/ba-p/1051123
https://www.youtube.com/watch?v=pnAesWxYgJ8