Calculation of data from different tables on Power BI (Dax)

Hello,

I am struggling with a calculation on Power BI.

Let's say you have two tables: 'Budget 2021' and 'Budget 2022', with the following data:

"Budget 2021" table:

Month Budget 1

January 265'444
February 325'000
March 125'000

"Budget 2022" table:

Month Budget 2

January 564'000
February 748'000
March 145'000

Therefore, I would like to have a simple formula (with the steps) that will allows me to calculate the total of each line of Budget with the result below on a new table:

Month Total Budget

January 829'444
February 1'073'000
March 270'000

You can also see the data of the pdf file.

I have tried different formulas below but none of them worked:

Total Budget = SUMX( UNION( ADDCOLUMNS('Budget 2021', "Budget 1", Budget 2021), ADDCOLUMNS('Budget 2022', "Budget 2", Budget 2022) ), [Budget] )
(I don't understand when the errors says that "ADDCOLUMNS" can not add the column "Budget 2" because it already exists)

SUMX( UNION( ADDCOLUMNS('Budget 2021', "Budget 1", Budget 2021), ADDCOLUMNS('Budget 2022', "Budget 2", Budget 2022) ), SUM('Budget 2021'[Budget 1]) + SUM('Budget 2022'[Budget 2]) )
And I have tried others but unfortunately, all of them failed.

I have also used functions like: Userelationship, Calculate, SUMX, and simple addition, etc. But probably without the right structure, which why my results didn't work as well.

In conclusion, I just want to calculate (add, subtract, divide, multiply) datas from different tables.

Is there anyone who can help me with a simple formula for beginner, please? With also the explanations/steps of the formula. Thanks in advance.